Добавьте файлы проекта.

src/Massenger.Client/App.xaml

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+<?xml version = "1.0" encoding = "UTF-8" ?>
+<Application xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:local="clr-namespace:Massenger.Client"
+             x:Class="Massenger.Client.App">
+    <Application.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceDictionary Source="Resources/Styles/Colors.xaml" />
+                <ResourceDictionary Source="Resources/Styles/Styles.xaml" />
+            </ResourceDictionary.MergedDictionaries>
+        </ResourceDictionary>
+    </Application.Resources>
+</Application>

src/Massenger.Client/App.xaml.cs

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+using Massenger.Client.Pages;
+using Massenger.Client.Services;
+
+namespace Massenger.Client;
+
+public partial class App : Application
+{
+    private readonly SessionService _sessionService;
+    private readonly RealtimeService _realtimeService;
+    private readonly IPushRegistrationService _pushRegistrationService;
+    private readonly NotificationActivationService _notificationActivationService;
+
+    public App()
+    {
+        InitializeComponent();
+
+        _sessionService = ServiceHelper.GetRequiredService<SessionService>();
+        _realtimeService = ServiceHelper.GetRequiredService<RealtimeService>();
+        _pushRegistrationService = ServiceHelper.GetRequiredService<IPushRegistrationService>();
+        _notificationActivationService = ServiceHelper.GetRequiredService<NotificationActivationService>();
+        _sessionService.SessionChanged += OnSessionChanged;
+        _notificationActivationService.ChatRequested += OnChatRequested;
+    }
+
+    protected override Window CreateWindow(IActivationState? activationState)
+    {
+        var window = new Window(new ContentPage
+        {
+            Content = new Grid
+            {
+                Children =
+                {
+                    new ActivityIndicator
+                    {
+                        IsRunning = true,
+                        HorizontalOptions = LayoutOptions.Center,
+                        VerticalOptions = LayoutOptions.Center
+                    }
+                }
+            }
+        });
+
+        _ = InitializeAsync(window);
+        return window;
+    }
+
+    private async Task InitializeAsync(Window window)
+    {
+        await _sessionService.RestoreAsync();
+        await _pushRegistrationService.InitializeAsync();
+        if (_sessionService.IsAuthenticated)
+        {
+            await _pushRegistrationService.RegisterCurrentDeviceAsync();
+            await _realtimeService.ConnectAsync();
+            await MainThread.InvokeOnMainThreadAsync(() => window.Page = new AppShell());
+            await NavigateToPendingChatAsync();
+            return;
+        }
+
+        await MainThread.InvokeOnMainThreadAsync(() => window.Page = new NavigationPage(new LoginPage()));
+    }
+
+    private async void OnSessionChanged(object? sender, EventArgs e)
+    {
+        if (Windows.Count == 0)
+        {
+            return;
+        }
+
+        var window = Windows[0];
+        if (_sessionService.IsAuthenticated)
+        {
+            await _pushRegistrationService.RegisterCurrentDeviceAsync();
+            await _realtimeService.ConnectAsync();
+            await MainThread.InvokeOnMainThreadAsync(() => window.Page = new AppShell());
+            await NavigateToPendingChatAsync();
+            return;
+        }
+
+        await _realtimeService.DisconnectAsync();
+        await MainThread.InvokeOnMainThreadAsync(() => window.Page = new NavigationPage(new LoginPage()));
+    }
+
+    private void OnChatRequested(object? sender, Guid chatId)
+    {
+        _ = NavigateToPendingChatAsync();
+    }
+
+    private Task NavigateToPendingChatAsync()
+    {
+        if (!_sessionService.IsAuthenticated)
+        {
+            return Task.CompletedTask;
+        }
+
+        var chatId = _notificationActivationService.ConsumePendingChat();
+        if (chatId is null)
+        {
+            return Task.CompletedTask;
+        }
+
+        return MainThread.InvokeOnMainThreadAsync(async () =>
+        {
+            if (Shell.Current is null)
+            {
+                _notificationActivationService.RestorePendingChat(chatId.Value);
+                return;
+            }
+
+            await Shell.Current.GoToAsync("//ChatsPage");
+            await Shell.Current.GoToAsync($"{nameof(ChatPage)}?chatId={chatId.Value}");
+        });
+    }
+}

src/Massenger.Client/AppShell.xaml

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+<?xml version="1.0" encoding="UTF-8" ?>
+<Shell
+    x:Class="Massenger.Client.AppShell"
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:pages="clr-namespace:Massenger.Client.Pages"
+    FlyoutBehavior="Disabled"
+    Shell.NavBarIsVisible="False"
+    Title="Massenger">
+
+    <TabBar>
+        <ShellContent
+            Title="Chats"
+            ContentTemplate="{DataTemplate pages:ChatsPage}"
+            Route="ChatsPage" />
+        <ShellContent
+            Title="Discover"
+            ContentTemplate="{DataTemplate pages:DiscoverPage}"
+            Route="DiscoverPage" />
+        <ShellContent
+            Title="Profile"
+            ContentTemplate="{DataTemplate pages:ProfilePage}"
+            Route="ProfilePage" />
+    </TabBar>
+
+</Shell>

src/Massenger.Client/AppShell.xaml.cs

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+using Massenger.Client.Pages;
+
+namespace Massenger.Client;
+
+public partial class AppShell : Shell
+{
+    public AppShell()
+    {
+        InitializeComponent();
+        Routing.RegisterRoute(nameof(ChatPage), typeof(ChatPage));
+    }
+}

src/Massenger.Client/Massenger.Client.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+	<PropertyGroup>
+		<TargetFrameworks>net10.0-android</TargetFrameworks>
+		<TargetFrameworks Condition="$([MSBuild]::IsOSPlatform('windows'))">$(TargetFrameworks);net10.0-windows10.0.19041.0</TargetFrameworks>
+
+		<OutputType>Exe</OutputType>
+		<RootNamespace>Massenger.Client</RootNamespace>
+		<UseMaui>true</UseMaui>
+		<SingleProject>true</SingleProject>
+		<ImplicitUsings>enable</ImplicitUsings>
+		<Nullable>enable</Nullable>
+
+		<!-- Enable XAML source generation for faster build times and improved performance.
+		     This generates C# code from XAML at compile time instead of runtime inflation.
+		     To disable, remove this line.
+		     For individual files, you can override by setting Inflator metadata:
+		       <MauiXaml Update="MyPage.xaml" Inflator="Default" /> (reverts to defaults: Runtime for Debug, XamlC for Release)
+		       <MauiXaml Update="MyPage.xaml" Inflator="Runtime" /> (force runtime inflation) -->
+		<MauiXamlInflator>SourceGen</MauiXamlInflator>
+
+		<!-- Display name -->
+		<ApplicationTitle>Massenger</ApplicationTitle>
+
+		<!-- App Identifier -->
+		<ApplicationId>com.seven.massenger</ApplicationId>
+
+		<!-- Versions -->
+		<ApplicationDisplayVersion>1.0</ApplicationDisplayVersion>
+		<ApplicationVersion>1</ApplicationVersion>
+
+		<!-- To develop, package, and publish an app to the Microsoft Store, see: https://aka.ms/MauiTemplateUnpackaged -->
+		<WindowsPackageType>None</WindowsPackageType>
+
+		<SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'android'">21.0</SupportedOSPlatformVersion>
+		<SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'windows'">10.0.17763.0</SupportedOSPlatformVersion>
+		<TargetPlatformMinVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'windows'">10.0.17763.0</TargetPlatformMinVersion>
+	</PropertyGroup>
+
+	<ItemGroup>
+		<!-- App Icon -->
+		<MauiIcon Include="Resources\AppIcon\appicon.svg" ForegroundFile="Resources\AppIcon\appiconfg.svg" Color="#0F766E" />
+
+		<!-- Splash Screen -->
+		<MauiSplashScreen Include="Resources\Splash\splash.svg" Color="#0F766E" BaseSize="128,128" />
+
+		<!-- Images -->
+		<MauiImage Include="Resources\Images\*" />
+		<MauiImage Update="Resources\Images\dotnet_bot.png" Resize="True" BaseSize="300,185" />
+		
+		<!-- Custom Fonts -->
+		<MauiFont Include="Resources\Fonts\*" />
+
+		<!-- Raw Assets (also remove the "Resources\Raw" prefix) -->
+		<MauiAsset Include="Resources\Raw\**" LogicalName="%(RecursiveDir)%(Filename)%(Extension)" />
+	</ItemGroup>
+
+	<ItemGroup>
+		<PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0" />
+		<PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="10.0.4" />
+		<PackageReference Include="Microsoft.Maui.Controls" Version="$(MauiVersion)" />
+		<PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="10.0.0" />
+	</ItemGroup>
+
+	<ItemGroup Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'android'">
+		<PackageReference Include="Xamarin.Firebase.Messaging" Version="124.0.0.2" />
+	</ItemGroup>
+
+	<ItemGroup>
+	  <ProjectReference Include="..\Massenger.Shared\Massenger.Shared.csproj" />
+	</ItemGroup>
+
+</Project>

src/Massenger.Client/MauiProgram.cs

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+using Microsoft.Extensions.Logging;
+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+
+namespace Massenger.Client;
+
+public static class MauiProgram
+{
+    public static MauiApp CreateMauiApp()
+    {
+        var builder = MauiApp.CreateBuilder();
+        builder
+            .UseMauiApp<App>()
+            .ConfigureFonts(fonts =>
+            {
+                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
+                fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
+            });
+
+        builder.Services.AddSingleton<ServerEndpointStore>();
+        builder.Services.AddSingleton<SessionService>();
+        builder.Services.AddSingleton<ApiClient>();
+        builder.Services.AddSingleton<RealtimeService>();
+        builder.Services.AddSingleton<NotificationActivationService>();
+#if ANDROID
+        builder.Services.AddSingleton<AndroidPushRegistrationService>();
+        builder.Services.AddSingleton<IPushRegistrationService>(sp => sp.GetRequiredService<AndroidPushRegistrationService>());
+#else
+        builder.Services.AddSingleton<IPushRegistrationService, NoOpPushRegistrationService>();
+#endif
+
+        builder.Services.AddTransient<LoginViewModel>();
+        builder.Services.AddTransient<ChatsViewModel>();
+        builder.Services.AddTransient<DiscoverViewModel>();
+        builder.Services.AddTransient<ChatViewModel>();
+        builder.Services.AddTransient<ProfileViewModel>();
+
+#if DEBUG
+        builder.Logging.AddDebug();
+#endif
+
+        var app = builder.Build();
+        ServiceHelper.Initialize(app.Services);
+        return app;
+    }
+}

src/Massenger.Client/Models/ChatAttachmentItem.cs

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+using Massenger.Shared;
+
+namespace Massenger.Client.Models;
+
+public sealed class ChatAttachmentItem(AttachmentDto attachment)
+{
+    public Guid Id { get; } = attachment.Id;
+
+    public string FileName { get; } = attachment.FileName;
+
+    public string ContentType { get; } = attachment.ContentType;
+
+    public long FileSizeBytes { get; } = attachment.FileSizeBytes;
+
+    public string DownloadPath { get; } = attachment.DownloadPath;
+
+    public AttachmentKind Kind { get; } = attachment.Kind;
+
+    public bool IsVoiceNote => Kind == AttachmentKind.VoiceNote;
+
+    public string DisplayText => IsVoiceNote
+        ? $"Voice note ({FormatFileSize(FileSizeBytes)})"
+        : $"{FileName} ({FormatFileSize(FileSizeBytes)})";
+
+    public string SecondaryText => IsVoiceNote ? FileName : ContentType;
+
+    public string ActionText => IsVoiceNote ? "Play" : "Open";
+
+    private static string FormatFileSize(long bytes)
+    {
+        const double kb = 1024;
+        const double mb = 1024 * 1024;
+
+        if (bytes >= mb)
+        {
+            return $"{bytes / mb:0.0} MB";
+        }
+
+        if (bytes >= kb)
+        {
+            return $"{bytes / kb:0.0} KB";
+        }
+
+        return $"{bytes} B";
+    }
+}

src/Massenger.Client/Models/ChatMessageItem.cs

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+using CommunityToolkit.Mvvm.ComponentModel;
+using Massenger.Shared;
+
+namespace Massenger.Client.Models;
+
+public partial class ChatMessageItem(MessageDto message, Guid currentUserId) : ObservableObject
+{
+    public Guid Id { get; } = message.Id;
+
+    public Guid ChatId { get; } = message.ChatId;
+
+    public DateTimeOffset SentAt { get; } = message.SentAt;
+
+    public string Author { get; } = message.Sender.DisplayName;
+
+    public string RawText { get; } = message.Text;
+
+    public bool IsDeleted { get; } = message.DeletedAt is not null;
+
+    public bool IsEdited { get; } = message.EditedAt is not null && message.DeletedAt is null;
+
+    public string Text => IsDeleted ? "Message removed." : RawText;
+
+    public bool HasText => IsDeleted || !string.IsNullOrWhiteSpace(Text);
+
+    public string Timestamp { get; } = message.SentAt.LocalDateTime.ToString("HH:mm");
+
+    public string StatusText => IsDeleted
+        ? $"{Timestamp} removed"
+        : IsEdited
+            ? $"{Timestamp} edited"
+            : Timestamp;
+
+    public bool IsMine { get; } = message.Sender.Id == currentUserId;
+
+    public string BubbleColor => IsMine ? "#0F766E" : "#E2E8F0";
+
+    public string TextColor => IsMine ? "#FFFFFF" : "#0F172A";
+
+    public LayoutOptions RowAlignment => IsMine ? LayoutOptions.End : LayoutOptions.Start;
+
+    public IReadOnlyList<ChatAttachmentItem> Attachments { get; } = message.Attachments
+        .Select(x => new ChatAttachmentItem(x))
+        .ToList();
+
+    public bool HasAttachments => !IsDeleted && Attachments.Count > 0;
+
+    public bool CanManage => IsMine && !IsDeleted;
+}

src/Massenger.Client/Models/ClientSession.cs

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+using Massenger.Shared;
+
+namespace Massenger.Client.Models;
+
+public sealed record ClientSession(
+    string AccessToken,
+    string RefreshToken,
+    DateTimeOffset AccessTokenExpiresAt,
+    UserSummaryDto User);

src/Massenger.Client/Models/DiscoverUserItem.cs

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+using CommunityToolkit.Mvvm.ComponentModel;
+using Massenger.Shared;
+
+namespace Massenger.Client.Models;
+
+public partial class DiscoverUserItem(UserSummaryDto user) : ObservableObject
+{
+    [ObservableProperty]
+    private bool isSelected;
+
+    public UserSummaryDto User { get; } = user;
+
+    public Guid Id => User.Id;
+
+    public string DisplayName => User.DisplayName;
+
+    public string Username => $"@{User.Username}";
+
+    public string Presence => User.IsOnline ? "online" : "offline";
+}

src/Massenger.Client/Models/PendingAttachmentItem.cs

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+using Microsoft.Maui.Storage;
+using Massenger.Shared;
+
+namespace Massenger.Client.Models;
+
+public sealed class PendingAttachmentItem
+{
+    private static readonly HashSet<string> AudioExtensions =
+    [
+        ".aac",
+        ".flac",
+        ".m4a",
+        ".mp3",
+        ".oga",
+        ".ogg",
+        ".opus",
+        ".wav",
+        ".webm"
+    ];
+
+    public PendingAttachmentItem(FileResult file, AttachmentKind kind)
+    {
+        File = file;
+        FileName = file.FileName;
+        ContentType = string.IsNullOrWhiteSpace(file.ContentType) ? "application/octet-stream" : file.ContentType;
+        Kind = kind;
+    }
+
+    public FileResult File { get; }
+
+    public string FileName { get; }
+
+    public string ContentType { get; }
+
+    public AttachmentKind Kind { get; }
+
+    public string DisplayName => Kind == AttachmentKind.VoiceNote ? $"Voice note: {FileName}" : FileName;
+
+    public static PendingAttachmentItem Create(FileResult file) =>
+        new(file, ResolveKind(file.FileName, file.ContentType));
+
+    public static bool IsVoiceFile(string? fileName, string? contentType) =>
+        ResolveKind(fileName, contentType) == AttachmentKind.VoiceNote;
+
+    private static AttachmentKind ResolveKind(string? fileName, string? contentType)
+    {
+        if (!string.IsNullOrWhiteSpace(contentType) &&
+            contentType.StartsWith("audio/", StringComparison.OrdinalIgnoreCase))
+        {
+            return AttachmentKind.VoiceNote;
+        }
+
+        var extension = Path.GetExtension(fileName ?? string.Empty);
+        return AudioExtensions.Contains(extension)
+            ? AttachmentKind.VoiceNote
+            : AttachmentKind.File;
+    }
+}

src/Massenger.Client/Pages/ChatPage.xaml

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+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage
+    x:Class="Massenger.Client.Pages.ChatPage"
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:models="clr-namespace:Massenger.Client.Models"
+    xmlns:viewModels="clr-namespace:Massenger.Client.ViewModels"
+    x:Name="ChatPageRoot"
+    Shell.NavBarIsVisible="True"
+    Title="{Binding Title}"
+    x:DataType="viewModels:ChatViewModel">
+
+    <Grid Padding="16" RowDefinitions="Auto,*,Auto" RowSpacing="14">
+        <Border Padding="16" StrokeShape="RoundRectangle 18">
+            <VerticalStackLayout Spacing="4">
+                <Label FontSize="24" FontAttributes="Bold" Text="{Binding Title}" />
+                <Label Text="{Binding Subtitle}" TextColor="#64748B" />
+            </VerticalStackLayout>
+        </Border>
+
+        <CollectionView Grid.Row="1" ItemsSource="{Binding Messages}">
+            <CollectionView.ItemTemplate>
+                <DataTemplate x:DataType="models:ChatMessageItem">
+                    <VerticalStackLayout Padding="0,0,0,12">
+                        <Border
+                            x:Name="MessageBubble"
+                            BackgroundColor="{Binding BubbleColor}"
+                            HorizontalOptions="{Binding RowAlignment}"
+                            Padding="14"
+                            StrokeShape="RoundRectangle 20">
+                            <VerticalStackLayout Spacing="4">
+                                <Label FontAttributes="Bold" Text="{Binding Author}" TextColor="{Binding TextColor}" />
+                                <Label IsVisible="{Binding HasText}" Text="{Binding Text}" TextColor="{Binding TextColor}" />
+                                <VerticalStackLayout
+                                    BindableLayout.ItemsSource="{Binding Attachments}"
+                                    IsVisible="{Binding HasAttachments}"
+                                    Spacing="8">
+                                    <BindableLayout.ItemTemplate>
+                                        <DataTemplate x:DataType="models:ChatAttachmentItem">
+                                            <Border BackgroundColor="#FFFFFF20" Padding="10" StrokeShape="RoundRectangle 12">
+                                                <Grid ColumnDefinitions="*,Auto" ColumnSpacing="8">
+                                                    <VerticalStackLayout Spacing="2">
+                                                        <Label FontAttributes="Bold" Text="{Binding DisplayText}" TextColor="{Binding Source={x:Reference MessageBubble}, Path=BindingContext.TextColor}" />
+                                                        <Label FontSize="12" Text="{Binding SecondaryText}" TextColor="{Binding Source={x:Reference MessageBubble}, Path=BindingContext.TextColor}" />
+                                                    </VerticalStackLayout>
+                                                    <Button
+                                                        Grid.Column="1"
+                                                        BackgroundColor="#00000020"
+                                                        Command="{Binding Source={x:Reference ChatPageRoot}, Path=BindingContext.OpenAttachmentCommand}"
+                                                        CommandParameter="{Binding .}"
+                                                        Text="{Binding ActionText}"
+                                                        TextColor="{Binding Source={x:Reference MessageBubble}, Path=BindingContext.TextColor}"
+                                                         />
+                                                </Grid>
+                                            </Border>
+                                        </DataTemplate>
+                                    </BindableLayout.ItemTemplate>
+                                </VerticalStackLayout>
+                                <HorizontalStackLayout IsVisible="{Binding CanManage}" HorizontalOptions="End" Spacing="8">
+                                    <Button
+                                        BackgroundColor="#00000020"
+                                        Command="{Binding Source={x:Reference ChatPageRoot}, Path=BindingContext.BeginEditMessageCommand}"
+                                        CommandParameter="{Binding .}"
+                                        Text="Edit"
+                                        TextColor="{Binding TextColor}" />
+                                    <Button
+                                        BackgroundColor="#7F1D1D"
+                                        Command="{Binding Source={x:Reference ChatPageRoot}, Path=BindingContext.DeleteMessageCommand}"
+                                        CommandParameter="{Binding .}"
+                                        Text="Delete"
+                                        TextColor="#FFFFFF" />
+                                </HorizontalStackLayout>
+                                <Label FontSize="12" HorizontalTextAlignment="End" Text="{Binding StatusText}" TextColor="{Binding TextColor}" />
+                            </VerticalStackLayout>
+                        </Border>
+                    </VerticalStackLayout>
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+        </CollectionView>
+
+        <VerticalStackLayout Grid.Row="2" Spacing="10">
+            <Border IsVisible="{Binding IsEditingMessage}" Padding="12" StrokeShape="RoundRectangle 14">
+                <Grid ColumnDefinitions="*,Auto" ColumnSpacing="8">
+                    <VerticalStackLayout Spacing="2">
+                        <Label FontAttributes="Bold" Text="Editing message" />
+                        <Label Text="{Binding EditingMessageBanner}" TextColor="#64748B" />
+                    </VerticalStackLayout>
+                    <Button Grid.Column="1" Command="{Binding CancelEditMessageCommand}" Text="Cancel" />
+                </Grid>
+            </Border>
+
+            <Border IsVisible="{Binding HasPendingAttachment}" Padding="12" StrokeShape="RoundRectangle 14">
+                <Grid ColumnDefinitions="*,Auto" ColumnSpacing="8">
+                    <VerticalStackLayout Spacing="2">
+                        <Label FontAttributes="Bold" Text="Pending attachment" />
+                        <Label Text="{Binding PendingAttachmentName}" TextColor="#64748B" />
+                    </VerticalStackLayout>
+                    <Button Grid.Column="1" Command="{Binding RemovePendingAttachmentCommand}" Text="Remove" />
+                </Grid>
+            </Border>
+
+            <Border IsVisible="{Binding ShowReadOnlyBanner}" BackgroundColor="#FFFBEB" Padding="12" StrokeShape="RoundRectangle 14">
+                <Label Text="This channel is read-only for subscribers. Only the owner can publish." TextColor="#92400E" />
+            </Border>
+
+            <Grid IsVisible="{Binding ShowComposer}" ColumnDefinitions="Auto,Auto,*,Auto" ColumnSpacing="12">
+                <Button Command="{Binding PickAttachmentCommand}" Text="Attach" />
+                <Button Grid.Column="1" Command="{Binding PickVoiceNoteCommand}" Text="Voice" />
+                <Editor Grid.Column="2" AutoSize="TextChanges" Placeholder="Write a message or add a file..." Text="{Binding DraftText}" />
+                <Button Grid.Column="3" Command="{Binding SendMessageCommand}" Text="Send" />
+            </Grid>
+
+            <Label IsVisible="{Binding HasError}" Text="{Binding ErrorMessage}" TextColor="#B91C1C" />
+        </VerticalStackLayout>
+    </Grid>
+</ContentPage>

src/Massenger.Client/Pages/ChatPage.xaml.cs

@@ -0,0 +1,44 @@
+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+
+namespace Massenger.Client.Pages;
+
+[QueryProperty(nameof(ChatId), "chatId")]
+public partial class ChatPage : ContentPage
+{
+    private readonly ChatViewModel _viewModel;
+
+    private string? _chatId;
+
+    public string? ChatId
+    {
+        get => _chatId;
+        set
+        {
+            _chatId = value;
+            _ = LoadChatAsync(value);
+        }
+    }
+
+    public ChatPage()
+    {
+        InitializeComponent();
+        _viewModel = ServiceHelper.GetRequiredService<ChatViewModel>();
+        _viewModel.AttachRealtime();
+        BindingContext = _viewModel;
+    }
+
+    protected override void OnDisappearing()
+    {
+        base.OnDisappearing();
+        _viewModel.DetachRealtime();
+    }
+
+    private async Task LoadChatAsync(string? chatId)
+    {
+        if (Guid.TryParse(chatId, out var parsed))
+        {
+            await _viewModel.LoadAsync(parsed);
+        }
+    }
+}

src/Massenger.Client/Pages/ChatsPage.xaml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage
+    x:Class="Massenger.Client.Pages.ChatsPage"
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:shared="clr-namespace:Massenger.Shared;assembly=Massenger.Shared"
+    xmlns:viewModels="clr-namespace:Massenger.Client.ViewModels"
+    x:DataType="viewModels:ChatsViewModel"
+    x:Name="RootPage">
+
+    <Grid Padding="20" RowDefinitions="Auto,*,Auto" RowSpacing="16">
+        <Grid ColumnDefinitions="*,Auto" ColumnSpacing="12">
+            <VerticalStackLayout Spacing="4">
+                <Label FontSize="28" FontAttributes="Bold" Text="Chats" />
+                <Label Text="Recent conversations are ordered by last activity." TextColor="#64748B" />
+            </VerticalStackLayout>
+            <Button Grid.Column="1" Command="{Binding LoadCommand}" Text="Refresh" />
+        </Grid>
+
+        <RefreshView Grid.Row="1" Command="{Binding LoadCommand}" IsRefreshing="{Binding IsBusy}">
+            <CollectionView
+                ItemsSource="{Binding Chats}"
+                SelectionChanged="OnSelectionChanged"
+                SelectionMode="Single">
+                <CollectionView.EmptyView>
+                    <VerticalStackLayout Padding="24" Spacing="6">
+                        <Label HorizontalTextAlignment="Center" Text="{Binding EmptyState}" TextColor="#64748B" />
+                    </VerticalStackLayout>
+                </CollectionView.EmptyView>
+                <CollectionView.ItemTemplate>
+                    <DataTemplate x:DataType="shared:ChatSummaryDto">
+                        <Border Margin="0,0,0,12" Padding="16" StrokeShape="RoundRectangle 18">
+                            <Grid ColumnDefinitions="*,Auto" RowDefinitions="Auto,Auto,Auto" RowSpacing="6">
+                                <Label FontAttributes="Bold" Text="{Binding Title}" />
+                            <Label Grid.Column="1" FontSize="12" Text="{Binding LastActivityAt, StringFormat='{}{0:HH:mm}'}" TextColor="#64748B" />
+                                <Label Grid.Row="1" Grid.ColumnSpan="2" Text="{Binding SecondaryText}" TextColor="#0F766E" />
+                                <Label Grid.Row="2" Grid.ColumnSpan="2" LineBreakMode="TailTruncation" Text="{Binding LastMessagePreview}" TextColor="#475569" />
+                            </Grid>
+                        </Border>
+                    </DataTemplate>
+                </CollectionView.ItemTemplate>
+            </CollectionView>
+        </RefreshView>
+
+        <Label Grid.Row="2" FontSize="12" Text="Use Discover to search users and create direct chats, groups or channels." TextColor="#94A3B8" />
+    </Grid>
+</ContentPage>

src/Massenger.Client/Pages/ChatsPage.xaml.cs

@@ -0,0 +1,32 @@
+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+using Massenger.Shared;
+
+namespace Massenger.Client.Pages;
+
+public partial class ChatsPage : ContentPage
+{
+    private ChatsViewModel ViewModel => (ChatsViewModel)BindingContext;
+
+    public ChatsPage()
+    {
+        InitializeComponent();
+        BindingContext = ServiceHelper.GetRequiredService<ChatsViewModel>();
+        ViewModel.AttachRealtime();
+    }
+
+    protected override async void OnAppearing()
+    {
+        base.OnAppearing();
+        await ViewModel.LoadAsync();
+    }
+
+    private async void OnSelectionChanged(object? sender, SelectionChangedEventArgs e)
+    {
+        if (e.CurrentSelection.FirstOrDefault() is ChatSummaryDto chat)
+        {
+            await ViewModel.OpenChatAsync(chat);
+            ((CollectionView)sender!).SelectedItem = null;
+        }
+    }
+}

src/Massenger.Client/Pages/DiscoverPage.xaml

@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage
+    x:Class="Massenger.Client.Pages.DiscoverPage"
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:models="clr-namespace:Massenger.Client.Models"
+    xmlns:viewModels="clr-namespace:Massenger.Client.ViewModels"
+    x:DataType="viewModels:DiscoverViewModel"
+    x:Name="RootPage">
+
+    <ScrollView>
+        <VerticalStackLayout Padding="20" Spacing="18">
+            <VerticalStackLayout Spacing="4">
+                <Label FontSize="28" FontAttributes="Bold" Text="Discover" />
+                <Label Text="Search teammates, open direct chats, assemble groups or create broadcast channels." TextColor="#64748B" />
+            </VerticalStackLayout>
+
+            <Grid ColumnDefinitions="*,Auto" ColumnSpacing="12">
+                <Entry Placeholder="Find by username or display name" Text="{Binding Query}" />
+                <Button Grid.Column="1" Command="{Binding SearchCommand}" Text="Search" />
+            </Grid>
+
+            <Border Padding="18" StrokeShape="RoundRectangle 20">
+                <VerticalStackLayout Spacing="12">
+                    <Grid ColumnDefinitions="*,Auto" ColumnSpacing="8">
+                        <Label FontAttributes="Bold" Text="Users" />
+                        <Label Grid.Column="1" Text="{Binding SelectedCount, StringFormat='Selected: {0}'}" TextColor="#64748B" />
+                    </Grid>
+
+                    <CollectionView ItemsSource="{Binding Results}">
+                        <CollectionView.ItemTemplate>
+                            <DataTemplate x:DataType="models:DiscoverUserItem">
+                                <Border Margin="0,0,0,10" Padding="14" StrokeShape="RoundRectangle 18">
+                                    <Grid ColumnDefinitions="Auto,*,Auto" ColumnSpacing="12">
+                                        <CheckBox IsChecked="{Binding IsSelected}" VerticalOptions="Center" />
+                                        <VerticalStackLayout Grid.Column="1" Spacing="2">
+                                            <Label FontAttributes="Bold" Text="{Binding DisplayName}" />
+                                            <Label FontSize="12" Text="{Binding Username}" TextColor="#64748B" />
+                                            <Label FontSize="12" Text="{Binding Presence}" TextColor="#0F766E" />
+                                        </VerticalStackLayout>
+                                        <Button
+                                            Grid.Column="2"
+                                            Command="{Binding Source={x:Reference RootPage}, Path=BindingContext.StartDirectChatCommand}"
+                                            CommandParameter="{Binding .}"
+                                            Text="Direct" />
+                                    </Grid>
+                                </Border>
+                            </DataTemplate>
+                        </CollectionView.ItemTemplate>
+                    </CollectionView>
+                </VerticalStackLayout>
+            </Border>
+
+            <Border BackgroundColor="#F8FAFC" Padding="18" StrokeShape="RoundRectangle 20">
+                <VerticalStackLayout Spacing="12">
+                    <Label FontAttributes="Bold" Text="Create group chat" />
+                    <Entry Placeholder="Group title" Text="{Binding GroupTitle}" />
+                    <Button Command="{Binding CreateGroupCommand}" Text="Create group" />
+                    <Label FontSize="12" Text="Select at least two users above, then create the room." TextColor="#64748B" />
+                </VerticalStackLayout>
+            </Border>
+
+            <Border BackgroundColor="#ECFEFF" Padding="18" StrokeShape="RoundRectangle 20">
+                <VerticalStackLayout Spacing="12">
+                    <Label FontAttributes="Bold" Text="Create channel" />
+                    <Entry Placeholder="Channel title" Text="{Binding ChannelTitle}" />
+                    <Button Command="{Binding CreateChannelCommand}" Text="Create channel" />
+                    <Label FontSize="12" Text="Selected users become subscribers. The channel creator is the only publisher." TextColor="#0F766E" />
+                </VerticalStackLayout>
+            </Border>
+
+            <Label IsVisible="{Binding HasError}" Text="{Binding ErrorMessage}" TextColor="#B91C1C" />
+        </VerticalStackLayout>
+    </ScrollView>
+</ContentPage>

src/Massenger.Client/Pages/DiscoverPage.xaml.cs

@@ -0,0 +1,24 @@
+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+
+namespace Massenger.Client.Pages;
+
+public partial class DiscoverPage : ContentPage
+{
+    private DiscoverViewModel ViewModel => (DiscoverViewModel)BindingContext;
+
+    public DiscoverPage()
+    {
+        InitializeComponent();
+        BindingContext = ServiceHelper.GetRequiredService<DiscoverViewModel>();
+    }
+
+    protected override async void OnAppearing()
+    {
+        base.OnAppearing();
+        if (ViewModel.Results.Count == 0)
+        {
+            await ViewModel.SearchAsync();
+        }
+    }
+}

src/Massenger.Client/Pages/LoginPage.xaml

@@ -0,0 +1,58 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage
+    x:Class="Massenger.Client.Pages.LoginPage"
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:viewModels="clr-namespace:Massenger.Client.ViewModels"
+    x:DataType="viewModels:LoginViewModel"
+    Title="Massenger">
+
+    <ContentPage.Background>
+        <LinearGradientBrush EndPoint="1,1">
+            <GradientStop Color="#F8FAFC" Offset="0" />
+            <GradientStop Color="#D1FAE5" Offset="1" />
+        </LinearGradientBrush>
+    </ContentPage.Background>
+
+    <ScrollView>
+        <VerticalStackLayout Padding="24,48,24,24" Spacing="24">
+            <VerticalStackLayout Spacing="8">
+                <Label FontSize="40" FontAttributes="Bold" Text="Massenger" TextColor="#0F172A" />
+                <Label Text="{Binding PageTitle}" TextColor="#334155" />
+                <Label Text="Core Telegram-like flow: auth, direct chats, groups, real-time delivery and shared history." TextColor="#475569" />
+            </VerticalStackLayout>
+
+            <Border BackgroundColor="{AppThemeBinding Light=White, Dark=#0F172A}" Padding="20" StrokeShape="RoundRectangle 24">
+                <VerticalStackLayout Spacing="16">
+                    <Label FontAttributes="Bold" Text="Server endpoint" />
+                    <Entry Placeholder="http://localhost:5099" Text="{Binding ServerUrl}" />
+
+                    <Grid ColumnDefinitions="*,Auto" ColumnSpacing="12">
+                        <VerticalStackLayout Grid.Column="0" Spacing="4">
+                            <Label FontAttributes="Bold" Text="Create account mode" />
+                            <Label FontSize="12" Text="Turn on only when you want to register a new user." TextColor="#64748B" />
+                        </VerticalStackLayout>
+                        <Switch Grid.Column="1" IsToggled="{Binding IsRegisterMode}" VerticalOptions="Center" />
+                    </Grid>
+
+                    <Entry Placeholder="Username" Text="{Binding Username}" />
+                    <Entry IsVisible="{Binding IsRegisterMode}" Placeholder="Display name" Text="{Binding DisplayName}" />
+                    <Entry IsPassword="True" Placeholder="Password" Text="{Binding Password}" />
+
+                    <Button Command="{Binding AuthenticateCommand}" Text="{Binding PrimaryActionText}" />
+
+                    <Label IsVisible="{Binding HasError}" Text="{Binding ErrorMessage}" TextColor="#B91C1C" />
+                </VerticalStackLayout>
+            </Border>
+
+            <Border BackgroundColor="#ECFEFF" Padding="20" StrokeShape="RoundRectangle 20">
+                <VerticalStackLayout Spacing="6">
+                    <Label FontAttributes="Bold" Text="Seeded demo users" TextColor="#0F172A" />
+                    <Label Text="alice / demo123" TextColor="#155E75" />
+                    <Label Text="bob / demo123" TextColor="#155E75" />
+                    <Label Text="carol / demo123" TextColor="#155E75" />
+                </VerticalStackLayout>
+            </Border>
+        </VerticalStackLayout>
+    </ScrollView>
+</ContentPage>

src/Massenger.Client/Pages/LoginPage.xaml.cs

@@ -0,0 +1,13 @@
+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+
+namespace Massenger.Client.Pages;
+
+public partial class LoginPage : ContentPage
+{
+    public LoginPage()
+    {
+        InitializeComponent();
+        BindingContext = ServiceHelper.GetRequiredService<LoginViewModel>();
+    }
+}

src/Massenger.Client/Pages/ProfilePage.xaml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage
+    x:Class="Massenger.Client.Pages.ProfilePage"
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:viewModels="clr-namespace:Massenger.Client.ViewModels"
+    x:DataType="viewModels:ProfileViewModel">
+
+    <ScrollView>
+        <VerticalStackLayout Padding="20" Spacing="18">
+            <VerticalStackLayout Spacing="4">
+                <Label FontSize="28" FontAttributes="Bold" Text="Profile" />
+                <Label Text="Account and connectivity settings." TextColor="#64748B" />
+            </VerticalStackLayout>
+
+            <Border BackgroundColor="#ECFEFF" Padding="18" StrokeShape="RoundRectangle 20">
+                <VerticalStackLayout Spacing="8">
+                    <Label FontSize="24" FontAttributes="Bold" Text="{Binding DisplayName}" />
+                    <Label Text="{Binding Username}" TextColor="#155E75" />
+                    <Label Text="{Binding ConnectionStatus, StringFormat='Realtime: {0}'}" TextColor="#0F766E" />
+                </VerticalStackLayout>
+            </Border>
+
+            <Border Padding="18" StrokeShape="RoundRectangle 20">
+                <VerticalStackLayout Spacing="12">
+                    <Label FontAttributes="Bold" Text="Server URL" />
+                    <Entry Placeholder="http://localhost:5099" Text="{Binding ServerUrl}" />
+                    <Grid ColumnDefinitions="*,*" ColumnSpacing="12">
+                        <Button Command="{Binding SaveServerCommand}" Text="Save and reconnect" />
+                        <Button Grid.Column="1" Command="{Binding RefreshProfileCommand}" Text="Refresh profile" />
+                    </Grid>
+                </VerticalStackLayout>
+            </Border>
+
+            <Button Command="{Binding LogoutCommand}" Text="Sign out" />
+            <Label IsVisible="{Binding HasError}" Text="{Binding ErrorMessage}" TextColor="#B91C1C" />
+        </VerticalStackLayout>
+    </ScrollView>
+</ContentPage>

src/Massenger.Client/Pages/ProfilePage.xaml.cs

@@ -0,0 +1,21 @@
+using Massenger.Client.Services;
+using Massenger.Client.ViewModels;
+
+namespace Massenger.Client.Pages;
+
+public partial class ProfilePage : ContentPage
+{
+    private ProfileViewModel ViewModel => (ProfileViewModel)BindingContext;
+
+    public ProfilePage()
+    {
+        InitializeComponent();
+        BindingContext = ServiceHelper.GetRequiredService<ProfileViewModel>();
+    }
+
+    protected override async void OnAppearing()
+    {
+        base.OnAppearing();
+        await ViewModel.LoadAsync();
+    }
+}

src/Massenger.Client/Platforms/Android/AndroidFirebaseOptionsLoader.cs

@@ -0,0 +1,47 @@
+using System.Text.Json;
+using Android.Content;
+
+namespace Massenger.Client;
+
+internal static class AndroidFirebaseOptionsLoader
+{
+    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);
+    private static AndroidFirebaseOptions? _cachedOptions;
+
+    public static AndroidFirebaseOptions? TryLoad(Context context)
+    {
+        if (_cachedOptions is not null)
+        {
+            return _cachedOptions;
+        }
+
+        try
+        {
+            using var stream = context.Assets!.Open("firebase.android.json");
+            using var reader = new StreamReader(stream);
+            var json = reader.ReadToEnd();
+            var options = JsonSerializer.Deserialize<AndroidFirebaseOptions>(json, JsonOptions);
+            if (options is null ||
+                string.IsNullOrWhiteSpace(options.ApplicationId) ||
+                string.IsNullOrWhiteSpace(options.ProjectId) ||
+                string.IsNullOrWhiteSpace(options.ApiKey) ||
+                string.IsNullOrWhiteSpace(options.SenderId))
+            {
+                return null;
+            }
+
+            _cachedOptions = options;
+            return _cachedOptions;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    internal sealed record AndroidFirebaseOptions(
+        string ApplicationId,
+        string ProjectId,
+        string ApiKey,
+        string SenderId);
+}

src/Massenger.Client/Platforms/Android/AndroidManifest.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+	<application android:allowBackup="true" android:icon="@mipmap/appicon" android:roundIcon="@mipmap/appicon_round" android:supportsRtl="true" android:usesCleartextTraffic="true"></application>
+	<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+	<uses-permission android:name="android.permission.INTERNET" />
+	<uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+</manifest>

src/Massenger.Client/Platforms/Android/AndroidNotificationDisplayService.cs

@@ -0,0 +1,59 @@
+using Android.App;
+using Android.Content;
+using AndroidX.Core.App;
+using Massenger.Shared;
+
+namespace Massenger.Client;
+
+internal static class AndroidNotificationDisplayService
+{
+    public static void Show(Context context, IDictionary<string, string> data)
+    {
+        if (!AndroidNotificationPermissionHelper.AreNotificationsEnabled(context))
+        {
+            return;
+        }
+
+        var title = data.TryGetValue(PushDataKeys.Title, out var rawTitle) && !string.IsNullOrWhiteSpace(rawTitle)
+            ? rawTitle
+            : "Massenger";
+        var body = data.TryGetValue(PushDataKeys.Body, out var rawBody) && !string.IsNullOrWhiteSpace(rawBody)
+            ? rawBody
+            : "New message";
+
+        var intent = new Intent(context, typeof(MainActivity))
+            .SetAction(AndroidPushBootstrapper.NotificationAction)
+            .AddFlags(ActivityFlags.SingleTop | ActivityFlags.ClearTop);
+
+        if (data.TryGetValue(PushDataKeys.ChatId, out var chatId))
+        {
+            intent.PutExtra(PushDataKeys.ChatId, chatId);
+        }
+
+        var requestCode = data.TryGetValue(PushDataKeys.MessageId, out var messageId)
+            ? messageId.GetHashCode(StringComparison.Ordinal)
+            : Environment.TickCount;
+
+        var pendingIntentFlags = OperatingSystem.IsAndroidVersionAtLeast(23)
+            ? PendingIntentFlags.UpdateCurrent | PendingIntentFlags.Immutable
+            : PendingIntentFlags.UpdateCurrent;
+
+        using var pendingIntent = PendingIntent.GetActivity(
+            context,
+            requestCode,
+            intent,
+            pendingIntentFlags);
+
+        var builder = new NotificationCompat.Builder(context, AndroidPushBootstrapper.NotificationChannelId);
+        builder.SetContentTitle(title);
+        builder.SetContentText(body);
+        builder.SetSmallIcon(Resource.Mipmap.appicon);
+        builder.SetAutoCancel(true);
+        builder.SetPriority((int)NotificationPriority.High);
+        builder.SetContentIntent(pendingIntent);
+
+        var notification = builder.Build();
+
+        NotificationManagerCompat.From(context)?.Notify(requestCode, notification);
+    }
+}

src/Massenger.Client/Platforms/Android/AndroidNotificationPermissionHelper.cs

@@ -0,0 +1,41 @@
+using Android;
+using Android.App;
+using Android.Content;
+using Android.Content.PM;
+using Android.OS;
+using AndroidX.Core.App;
+
+namespace Massenger.Client;
+
+internal static class AndroidNotificationPermissionHelper
+{
+    private const string PostNotificationsPermission = "android.permission.POST_NOTIFICATIONS";
+
+    public const int RequestCode = 5101;
+
+    public static bool AreNotificationsEnabled(Context context)
+    {
+        if (OperatingSystem.IsAndroidVersionAtLeast(33) &&
+            context.CheckSelfPermission(PostNotificationsPermission) != Permission.Granted)
+        {
+            return false;
+        }
+
+        return NotificationManagerCompat.From(context)?.AreNotificationsEnabled() ?? false;
+    }
+
+    public static void RequestIfNeeded(Activity activity)
+    {
+        if (!OperatingSystem.IsAndroidVersionAtLeast(33))
+        {
+            return;
+        }
+
+        if (activity.CheckSelfPermission(PostNotificationsPermission) == Permission.Granted)
+        {
+            return;
+        }
+
+        activity.RequestPermissions([PostNotificationsPermission], RequestCode);
+    }
+}

src/Massenger.Client/Platforms/Android/AndroidPushBootstrapper.cs

@@ -0,0 +1,96 @@
+using Android.App;
+using Android.Content;
+using Android.OS;
+using Firebase;
+
+namespace Massenger.Client;
+
+internal static class AndroidPushBootstrapper
+{
+    public const string NotificationAction = "com.seven.massenger.OPEN_CHAT";
+    public const string NotificationChannelId = "massenger_messages";
+
+    private static bool _attemptedInitialization;
+
+    public static bool TryInitialize(Context context)
+    {
+        if (_attemptedInitialization)
+        {
+            EnsureNotificationChannel(context);
+            return FirebaseApp.InitializeApp(context) is not null || TryGetExistingApp() is not null;
+        }
+
+        _attemptedInitialization = true;
+
+        var existingApp = TryGetExistingApp();
+        if (existingApp is not null)
+        {
+            EnsureNotificationChannel(context);
+            return true;
+        }
+
+        if (FirebaseApp.InitializeApp(context) is not null)
+        {
+            EnsureNotificationChannel(context);
+            return true;
+        }
+
+        var options = AndroidFirebaseOptionsLoader.TryLoad(context);
+        if (options is null)
+        {
+            return false;
+        }
+
+        var firebaseOptions = new FirebaseOptions.Builder()
+            .SetApplicationId(options.ApplicationId)
+            .SetProjectId(options.ProjectId)
+            .SetApiKey(options.ApiKey)
+            .SetGcmSenderId(options.SenderId)
+            .Build();
+
+        var createdApp = FirebaseApp.InitializeApp(context, firebaseOptions);
+        if (createdApp is null)
+        {
+            return false;
+        }
+
+        EnsureNotificationChannel(context);
+        return true;
+    }
+
+    public static void EnsureNotificationChannel(Context context)
+    {
+        if (!OperatingSystem.IsAndroidVersionAtLeast(26))
+        {
+            return;
+        }
+
+        var manager = (NotificationManager?)context.GetSystemService(Context.NotificationService);
+        if (manager?.GetNotificationChannel(NotificationChannelId) is not null)
+        {
+            return;
+        }
+
+        var channel = new NotificationChannel(
+            NotificationChannelId,
+            "Messages",
+            NotificationImportance.High)
+        {
+            Description = "Chat message notifications"
+        };
+
+        manager?.CreateNotificationChannel(channel);
+    }
+
+    private static FirebaseApp? TryGetExistingApp()
+    {
+        try
+        {
+            return FirebaseApp.Instance;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+}

src/Massenger.Client/Platforms/Android/AndroidPushSettings.cs

@@ -0,0 +1,40 @@
+using Android.App;
+using Android.Content;
+
+namespace Massenger.Client;
+
+internal static class AndroidPushSettings
+{
+    private const string PreferencesName = "massenger_push";
+    private const string InstallationIdKey = "installation_id";
+    private const string DeviceTokenKey = "device_token";
+
+    public static string GetInstallationId()
+    {
+        var preferences = GetPreferences();
+        var installationId = preferences.GetString(InstallationIdKey, null);
+        if (!string.IsNullOrWhiteSpace(installationId))
+        {
+            return installationId;
+        }
+
+        installationId = Guid.NewGuid().ToString("N");
+        using var editor = preferences.Edit() ?? throw new InvalidOperationException("Android preferences editor is unavailable.");
+        editor.PutString(InstallationIdKey, installationId);
+        editor.Apply();
+        return installationId;
+    }
+
+    public static string? GetDeviceToken() =>
+        GetPreferences().GetString(DeviceTokenKey, null);
+
+    public static void SetDeviceToken(string token)
+    {
+        using var editor = GetPreferences().Edit() ?? throw new InvalidOperationException("Android preferences editor is unavailable.");
+        editor.PutString(DeviceTokenKey, token);
+        editor.Apply();
+    }
+
+    private static ISharedPreferences GetPreferences() =>
+        Android.App.Application.Context.GetSharedPreferences(PreferencesName, FileCreationMode.Private)!;
+}

src/Massenger.Client/Platforms/Android/AndroidTaskExtensions.cs

@@ -0,0 +1,40 @@
+using Android.Gms.Tasks;
+
+namespace Massenger.Client;
+
+internal static class AndroidTaskExtensions
+{
+    public static Task<string?> AsStringAsync(this Android.Gms.Tasks.Task task, System.Threading.CancellationToken cancellationToken = default)
+    {
+        var taskCompletionSource = new TaskCompletionSource<string?>(TaskCreationOptions.RunContinuationsAsynchronously);
+        if (cancellationToken.CanBeCanceled)
+        {
+            cancellationToken.Register(() => taskCompletionSource.TrySetCanceled(cancellationToken));
+        }
+
+        task.AddOnCompleteListener(new TaskCompletionListener(taskCompletionSource));
+        return taskCompletionSource.Task;
+    }
+
+    private sealed class TaskCompletionListener(TaskCompletionSource<string?> taskCompletionSource)
+        : Java.Lang.Object,
+          IOnCompleteListener
+    {
+        public void OnComplete(Android.Gms.Tasks.Task task)
+        {
+            if (task.IsCanceled)
+            {
+                taskCompletionSource.TrySetCanceled();
+                return;
+            }
+
+            if (!task.IsSuccessful)
+            {
+                taskCompletionSource.TrySetException(new InvalidOperationException(task.Exception?.Message ?? "Android task failed."));
+                return;
+            }
+
+            taskCompletionSource.TrySetResult(task.Result?.ToString());
+        }
+    }
+}

src/Massenger.Client/Platforms/Android/FirebaseTokenProvider.cs

@@ -0,0 +1,17 @@
+using Android.App;
+using Firebase.Messaging;
+
+namespace Massenger.Client;
+
+internal static class FirebaseTokenProvider
+{
+    public static async Task<string?> TryGetTokenAsync(CancellationToken cancellationToken = default)
+    {
+        if (!AndroidPushBootstrapper.TryInitialize(Android.App.Application.Context))
+        {
+            return null;
+        }
+
+        return await FirebaseMessaging.Instance.GetToken().AsStringAsync(cancellationToken);
+    }
+}

src/Massenger.Client/Platforms/Android/MainActivity.cs

@@ -0,0 +1,59 @@
+using Android.App;
+using Android.Content;
+using Android.Content.PM;
+using Android.OS;
+using System.Runtime.Versioning;
+using Massenger.Client.Services;
+using Massenger.Shared;
+
+namespace Massenger.Client;
+
+[Activity(Theme = "@style/Maui.SplashTheme", MainLauncher = true, LaunchMode = LaunchMode.SingleTop, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize | ConfigChanges.Density)]
+public class MainActivity : MauiAppCompatActivity
+{
+    protected override void OnCreate(Bundle? savedInstanceState)
+    {
+        base.OnCreate(savedInstanceState);
+        AndroidNotificationPermissionHelper.RequestIfNeeded(this);
+        HandleNotificationIntent(Intent);
+    }
+
+    protected override void OnNewIntent(Intent? intent)
+    {
+        base.OnNewIntent(intent);
+        if (intent is null)
+        {
+            return;
+        }
+
+        Intent = intent;
+        HandleNotificationIntent(intent);
+    }
+
+    [SupportedOSPlatform("android23.0")]
+    public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults)
+    {
+        base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
+
+        if (requestCode != AndroidNotificationPermissionHelper.RequestCode ||
+            grantResults.Length == 0 ||
+            grantResults[0] != Permission.Granted)
+        {
+            return;
+        }
+
+        _ = ServiceHelper.GetService<AndroidPushRegistrationService>()?.RegisterCurrentDeviceAsync() ?? Task.CompletedTask;
+    }
+
+    private static void HandleNotificationIntent(Intent? intent)
+    {
+        var chatIdRaw = intent?.GetStringExtra(PushDataKeys.ChatId);
+        if (!Guid.TryParse(chatIdRaw, out var chatId))
+        {
+            return;
+        }
+
+        ServiceHelper.GetService<NotificationActivationService>()?.SetPendingChat(chatId);
+        intent?.RemoveExtra(PushDataKeys.ChatId);
+    }
+}

src/Massenger.Client/Platforms/Android/MainApplication.cs

@@ -0,0 +1,21 @@
+using Android.App;
+using Android.Runtime;
+
+namespace Massenger.Client;
+
+[Application]
+public class MainApplication : MauiApplication
+{
+	public MainApplication(IntPtr handle, JniHandleOwnership ownership)
+		: base(handle, ownership)
+	{
+	}
+
+    public override void OnCreate()
+    {
+        base.OnCreate();
+        AndroidPushBootstrapper.TryInitialize(this);
+    }
+
+	protected override MauiApp CreateMauiApp() => MauiProgram.CreateMauiApp();
+}

src/Massenger.Client/Platforms/Android/MassengerFirebaseMessagingService.cs

@@ -0,0 +1,40 @@
+using Android.App;
+using Android.Content;
+using Firebase.Messaging;
+using Massenger.Client.Services;
+
+namespace Massenger.Client;
+
+[Service(Exported = false, Name = "com.seven.massenger.MassengerFirebaseMessagingService")]
+[IntentFilter(new[] { "com.google.firebase.MESSAGING_EVENT" })]
+public sealed class MassengerFirebaseMessagingService : FirebaseMessagingService
+{
+    public override void OnNewToken(string token)
+    {
+        base.OnNewToken(token);
+        AndroidPushSettings.SetDeviceToken(token);
+        _ = ServiceHelper.GetService<AndroidPushRegistrationService>()?.OnTokenRefreshedAsync(token) ?? Task.CompletedTask;
+    }
+
+    public override void OnMessageReceived(RemoteMessage message)
+    {
+        base.OnMessageReceived(message);
+        AndroidPushBootstrapper.EnsureNotificationChannel(this);
+
+        if (message.Data?.Count > 0)
+        {
+            AndroidNotificationDisplayService.Show(this, message.Data);
+            return;
+        }
+
+        var title = message.GetNotification()?.Title;
+        var body = message.GetNotification()?.Body;
+        AndroidNotificationDisplayService.Show(
+            this,
+            new Dictionary<string, string>
+            {
+                ["title"] = title ?? "Massenger",
+                ["body"] = body ?? "New message"
+            });
+    }
+}

src/Massenger.Client/Platforms/Android/Resources/values/colors.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="colorPrimary">#0F766E</color>
+    <color name="colorPrimaryDark">#115E59</color>
+    <color name="colorAccent">#115E59</color>
+</resources>

src/Massenger.Client/Platforms/Android/Services/AndroidPushRegistrationService.cs

@@ -0,0 +1,102 @@
+using Android.App;
+using Android.OS;
+using Microsoft.Extensions.Logging;
+using Massenger.Shared;
+
+namespace Massenger.Client.Services;
+
+public sealed class AndroidPushRegistrationService(
+    ApiClient apiClient,
+    SessionService sessionService,
+    ILogger<AndroidPushRegistrationService> logger) : IPushRegistrationService
+{
+    public Task InitializeAsync(CancellationToken cancellationToken = default)
+    {
+        AndroidPushBootstrapper.TryInitialize(Android.App.Application.Context);
+        return Task.CompletedTask;
+    }
+
+    public async Task RegisterCurrentDeviceAsync(CancellationToken cancellationToken = default)
+    {
+        if (!sessionService.IsAuthenticated)
+        {
+            return;
+        }
+
+        if (!AndroidPushBootstrapper.TryInitialize(Android.App.Application.Context))
+        {
+            logger.LogDebug("Android push configuration was not found. Device registration skipped.");
+            return;
+        }
+
+        var token = AndroidPushSettings.GetDeviceToken();
+        if (string.IsNullOrWhiteSpace(token))
+        {
+            try
+            {
+                token = await FirebaseTokenProvider.TryGetTokenAsync(cancellationToken);
+            }
+            catch (Exception ex)
+            {
+                logger.LogWarning(ex, "Failed to obtain Android FCM device token.");
+                return;
+            }
+        }
+
+        if (string.IsNullOrWhiteSpace(token))
+        {
+            return;
+        }
+
+        AndroidPushSettings.SetDeviceToken(token);
+
+        var request = new RegisterPushDeviceRequest(
+            PushPlatform.Android,
+            AndroidPushSettings.GetInstallationId(),
+            token,
+            BuildDeviceName(),
+            AndroidNotificationPermissionHelper.AreNotificationsEnabled(Android.App.Application.Context));
+
+        await apiClient.RegisterPushDeviceAsync(request, cancellationToken);
+    }
+
+    public async Task UnregisterCurrentDeviceAsync(CancellationToken cancellationToken = default)
+    {
+        if (!sessionService.IsAuthenticated)
+        {
+            return;
+        }
+
+        await apiClient.UnregisterPushDeviceAsync(AndroidPushSettings.GetInstallationId(), cancellationToken);
+    }
+
+    public async Task OnTokenRefreshedAsync(string token, CancellationToken cancellationToken = default)
+    {
+        if (string.IsNullOrWhiteSpace(token))
+        {
+            return;
+        }
+
+        AndroidPushSettings.SetDeviceToken(token);
+        if (!sessionService.IsAuthenticated)
+        {
+            return;
+        }
+
+        try
+        {
+            await RegisterCurrentDeviceAsync(cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            logger.LogWarning(ex, "Failed to sync refreshed Android FCM token.");
+        }
+    }
+
+    private static string BuildDeviceName()
+    {
+        var manufacturer = Build.Manufacturer ?? "Android";
+        var model = Build.Model ?? "device";
+        return $"{manufacturer} {model}".Trim();
+    }
+}

src/Massenger.Client/Platforms/MacCatalyst/AppDelegate.cs

@@ -0,0 +1,9 @@
+using Foundation;
+
+namespace Massenger.Client;
+
+[Register("AppDelegate")]
+public class AppDelegate : MauiUIApplicationDelegate
+{
+	protected override MauiApp CreateMauiApp() => MauiProgram.CreateMauiApp();
+}

src/Massenger.Client/Platforms/MacCatalyst/Entitlements.plist

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+    <!-- See https://aka.ms/maui-publish-app-store#add-entitlements for more information about adding entitlements.-->
+    <dict>
+        <!-- App Sandbox must be enabled to distribute a MacCatalyst app through the Mac App Store. -->
+        <key>com.apple.security.app-sandbox</key>
+        <true/>
+        <!-- When App Sandbox is enabled, this value is required to open outgoing network connections. -->
+        <key>com.apple.security.network.client</key>
+        <true/>
+    </dict>
+</plist>
+

src/Massenger.Client/Platforms/MacCatalyst/Info.plist

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <!-- The Mac App Store requires you specify if the app uses encryption. -->
+    <!-- Please consult https://developer.apple.com/documentation/bundleresources/information_property_list/itsappusesnonexemptencryption -->
+    <!-- <key>ITSAppUsesNonExemptEncryption</key> -->
+    <!-- Please indicate <true/> or <false/> here. -->
+
+    <!-- Specify the category for your app here. -->
+    <!-- Please consult https://developer.apple.com/documentation/bundleresources/information_property_list/lsapplicationcategorytype -->
+    <!-- <key>LSApplicationCategoryType</key> -->
+    <!-- <string>public.app-category.YOUR-CATEGORY-HERE</string> -->
+	<key>UIDeviceFamily</key>
+	<array>
+		<integer>2</integer>
+	</array>
+	<key>LSApplicationCategoryType</key>
+	<string>public.app-category.lifestyle</string>
+	<key>UIRequiredDeviceCapabilities</key>
+	<array>
+		<string>arm64</string>
+	</array>
+	<key>UISupportedInterfaceOrientations</key>
+	<array>
+		<string>UIInterfaceOrientationPortrait</string>
+		<string>UIInterfaceOrientationLandscapeLeft</string>
+		<string>UIInterfaceOrientationLandscapeRight</string>
+	</array>
+	<key>UISupportedInterfaceOrientations~ipad</key>
+	<array>
+		<string>UIInterfaceOrientationPortrait</string>
+		<string>UIInterfaceOrientationPortraitUpsideDown</string>
+		<string>UIInterfaceOrientationLandscapeLeft</string>
+		<string>UIInterfaceOrientationLandscapeRight</string>
+	</array>
+	<key>XSAppIconAssets</key>
+	<string>Assets.xcassets/appicon.appiconset</string>
+</dict>
+</plist>

src/Massenger.Client/Platforms/MacCatalyst/Program.cs

@@ -0,0 +1,15 @@
+using ObjCRuntime;
+using UIKit;
+
+namespace Massenger.Client;
+
+public class Program
+{
+	// This is the main entry point of the application.
+	static void Main(string[] args)
+	{
+		// if you want to use a different Application Delegate class from "AppDelegate"
+		// you can specify it here.
+		UIApplication.Main(args, null, typeof(AppDelegate));
+	}
+}

src/Massenger.Client/Platforms/Windows/App.xaml

@@ -0,0 +1,8 @@
+<maui:MauiWinUIApplication
+    x:Class="Massenger.Client.WinUI.App"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:maui="using:Microsoft.Maui"
+    xmlns:local="using:Massenger.Client.WinUI">
+
+</maui:MauiWinUIApplication>

src/Massenger.Client/Platforms/Windows/App.xaml.cs

@@ -0,0 +1,24 @@
+using Microsoft.UI.Xaml;
+
+// To learn more about WinUI, the WinUI project structure,
+// and more about our project templates, see: http://aka.ms/winui-project-info.
+
+namespace Massenger.Client.WinUI;
+
+/// <summary>
+/// Provides application-specific behavior to supplement the default Application class.
+/// </summary>
+public partial class App : MauiWinUIApplication
+{
+	/// <summary>
+	/// Initializes the singleton application object.  This is the first line of authored code
+	/// executed, and as such is the logical equivalent of main() or WinMain().
+	/// </summary>
+	public App()
+	{
+		this.InitializeComponent();
+	}
+
+	protected override MauiApp CreateMauiApp() => MauiProgram.CreateMauiApp();
+}
+

src/Massenger.Client/Platforms/Windows/Package.appxmanifest

@@ -0,0 +1,46 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Package
+  xmlns="http://schemas.microsoft.com/appx/manifest/foundation/windows10"
+  xmlns:uap="http://schemas.microsoft.com/appx/manifest/uap/windows10"
+  xmlns:mp="http://schemas.microsoft.com/appx/2014/phone/manifest"
+  xmlns:rescap="http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities"
+  IgnorableNamespaces="uap rescap">
+
+  <Identity Name="maui-package-name-placeholder" Publisher="CN=User Name" Version="0.0.0.0" />
+
+  <mp:PhoneIdentity PhoneProductId="707E1EB5-AB6F-4E2D-865F-42E17A9AB4F9" PhonePublisherId="00000000-0000-0000-0000-000000000000"/>
+
+  <Properties>
+    <DisplayName>$placeholder$</DisplayName>
+    <PublisherDisplayName>User Name</PublisherDisplayName>
+    <Logo>$placeholder$.png</Logo>
+  </Properties>
+
+  <Dependencies>
+    <TargetDeviceFamily Name="Windows.Universal" MinVersion="10.0.17763.0" MaxVersionTested="10.0.19041.0" />
+    <TargetDeviceFamily Name="Windows.Desktop" MinVersion="10.0.17763.0" MaxVersionTested="10.0.19041.0" />
+  </Dependencies>
+
+  <Resources>
+    <Resource Language="x-generate" />
+  </Resources>
+
+  <Applications>
+    <Application Id="App" Executable="$targetnametoken$.exe" EntryPoint="$targetentrypoint$">
+      <uap:VisualElements
+        DisplayName="$placeholder$"
+        Description="$placeholder$"
+        Square150x150Logo="$placeholder$.png"
+        Square44x44Logo="$placeholder$.png"
+        BackgroundColor="transparent">
+        <uap:DefaultTile Square71x71Logo="$placeholder$.png" Wide310x150Logo="$placeholder$.png" Square310x310Logo="$placeholder$.png" />
+        <uap:SplashScreen Image="$placeholder$.png" />
+      </uap:VisualElements>
+    </Application>
+  </Applications>
+
+  <Capabilities>
+    <rescap:Capability Name="runFullTrust" />
+  </Capabilities>
+
+</Package>

src/Massenger.Client/Platforms/Windows/app.manifest

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
+  <assemblyIdentity version="1.0.0.0" name="Massenger.Client.WinUI.app"/>
+
+  <application xmlns="urn:schemas-microsoft-com:asm.v3">
+    <windowsSettings>
+      <!-- The combination of below two tags have the following effect:
+           1) Per-Monitor for >= Windows 10 Anniversary Update
+           2) System < Windows 10 Anniversary Update
+      -->
+      <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true/PM</dpiAware>
+      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2, PerMonitor</dpiAwareness>
+
+      <longPathAware xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">true</longPathAware>
+    </windowsSettings>
+  </application>
+</assembly>

src/Massenger.Client/Platforms/iOS/AppDelegate.cs

@@ -0,0 +1,9 @@
+using Foundation;
+
+namespace Massenger.Client;
+
+[Register("AppDelegate")]
+public class AppDelegate : MauiUIApplicationDelegate
+{
+	protected override MauiApp CreateMauiApp() => MauiProgram.CreateMauiApp();
+}

src/Massenger.Client/Platforms/iOS/Info.plist

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>LSRequiresIPhoneOS</key>
+	<true/>
+	<key>UIDeviceFamily</key>
+	<array>
+		<integer>1</integer>
+		<integer>2</integer>
+	</array>
+	<key>UIRequiredDeviceCapabilities</key>
+	<array>
+		<string>arm64</string>
+	</array>
+	<key>UISupportedInterfaceOrientations</key>
+	<array>
+		<string>UIInterfaceOrientationPortrait</string>
+		<string>UIInterfaceOrientationLandscapeLeft</string>
+		<string>UIInterfaceOrientationLandscapeRight</string>
+	</array>
+	<key>UISupportedInterfaceOrientations~ipad</key>
+	<array>
+		<string>UIInterfaceOrientationPortrait</string>
+		<string>UIInterfaceOrientationPortraitUpsideDown</string>
+		<string>UIInterfaceOrientationLandscapeLeft</string>
+		<string>UIInterfaceOrientationLandscapeRight</string>
+	</array>
+	<key>XSAppIconAssets</key>
+	<string>Assets.xcassets/appicon.appiconset</string>
+</dict>
+</plist>

src/Massenger.Client/Platforms/iOS/Program.cs

@@ -0,0 +1,15 @@
+using ObjCRuntime;
+using UIKit;
+
+namespace Massenger.Client;
+
+public class Program
+{
+	// This is the main entry point of the application.
+	static void Main(string[] args)
+	{
+		// if you want to use a different Application Delegate class from "AppDelegate"
+		// you can specify it here.
+		UIApplication.Main(args, null, typeof(AppDelegate));
+	}
+}

src/Massenger.Client/Platforms/iOS/Resources/PrivacyInfo.xcprivacy

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+This is the minimum required version of the Apple Privacy Manifest for .NET MAUI apps.
+The contents below are needed because of APIs that are used in the .NET framework and .NET MAUI SDK.
+
+You are responsible for adding extra entries as needed for your application.
+
+More information: https://aka.ms/maui-privacy-manifest
+-->
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>NSPrivacyAccessedAPITypes</key>
+    <array>
+        <dict>
+            <key>NSPrivacyAccessedAPIType</key>
+            <string>NSPrivacyAccessedAPICategoryFileTimestamp</string>
+            <key>NSPrivacyAccessedAPITypeReasons</key>
+            <array>
+                <string>C617.1</string>
+            </array>
+        </dict>
+        <dict>
+            <key>NSPrivacyAccessedAPIType</key>
+            <string>NSPrivacyAccessedAPICategorySystemBootTime</string>
+            <key>NSPrivacyAccessedAPITypeReasons</key>
+            <array>
+                <string>35F9.1</string>
+            </array>
+        </dict>
+        <dict>
+            <key>NSPrivacyAccessedAPIType</key>
+            <string>NSPrivacyAccessedAPICategoryDiskSpace</string>
+            <key>NSPrivacyAccessedAPITypeReasons</key>
+            <array>
+                <string>E174.1</string>
+            </array>
+        </dict>
+        <!--
+            The entry below is only needed when you're using the Preferences API in your app.
+        <dict>
+            <key>NSPrivacyAccessedAPIType</key>
+            <string>NSPrivacyAccessedAPICategoryUserDefaults</string>
+            <key>NSPrivacyAccessedAPITypeReasons</key>
+            <array>
+                <string>CA92.1</string>
+            </array>
+        </dict> -->
+    </array>
+</dict>
+</plist>

src/Massenger.Client/Properties/launchSettings.json

@@ -0,0 +1,8 @@
+{
+  "profiles": {
+    "Windows Machine": {
+      "commandName": "Project",
+      "nativeDebugging": false
+    }
+  }
+}

src/Massenger.Client/Resources/AppIcon/appicon.svg

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg width="456" height="456" viewBox="0 0 456 456" version="1.1" xmlns="http://www.w3.org/2000/svg">
+    <rect x="0" y="0" width="456" height="456" fill="#512BD4" />
+</svg>

src/Massenger.Client/Resources/AppIcon/appiconfg.svg

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg width="456" height="456" viewBox="0 0 456 456" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xml:space="preserve" xmlns:serif="http://www.serif.com/" style="fill-rule:evenodd;clip-rule:evenodd;stroke-linejoin:round;stroke-miterlimit:2;">
+    <path d="m 105.50037,281.60863 c -2.70293,0 -5.00091,-0.90042 -6.893127,-2.70209 -1.892214,-1.84778 -2.837901,-4.04181 -2.837901,-6.58209 0,-2.58722 0.945687,-4.80389 2.837901,-6.65167 1.892217,-1.84778 4.190197,-2.77167 6.893127,-2.77167 2.74819,0 5.06798,0.92389 6.96019,2.77167 1.93749,1.84778 2.90581,4.06445 2.90581,6.65167 0,2.54028 -0.96832,4.73431 -2.90581,6.58209 -1.89221,1.80167 -4.212,2.70209 -6.96019,2.70209 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+    <path d="M 213.56111,280.08446 H 195.99044 L 149.69953,207.0544 c -1.17121,-1.84778 -2.14037,-3.76515 -2.90581,-5.75126 h -0.40578 c 0.36051,2.12528 0.54076,6.67515 0.54076,13.6496 v 65.13172 h -15.54349 v -99.36009 h 18.71925 l 44.7374,71.29798 c 1.89222,2.95695 3.1087,4.98917 3.64945,6.09751 h 0.26996 c -0.45021,-2.6325 -0.67573,-7.09015 -0.67573,-13.37293 v -64.02256 h 15.47557 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+    <path d="m 289.25134,280.08446 h -54.40052 v -99.36009 h 52.23835 v 13.99669 h -36.15411 v 28.13085 h 33.31621 v 13.9271 h -33.31621 v 29.37835 h 38.31628 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+    <path d="M 366.56466,194.72106 H 338.7222 v 85.3634 h -16.08423 v -85.3634 h -27.77455 v -13.99669 h 71.70124 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+</svg>

src/Massenger.Client/Resources/Raw/AboutAssets.txt

@@ -0,0 +1,15 @@
+Any raw assets you want to be deployed with your application can be placed in
+this directory (and child directories). Deployment of the asset to your application
+is automatically handled by the following `MauiAsset` Build Action within your `.csproj`.
+
+	<MauiAsset Include="Resources\Raw\**" LogicalName="%(RecursiveDir)%(Filename)%(Extension)" />
+
+These files will be deployed with your package and will be accessible using Essentials:
+
+	async Task LoadMauiAsset()
+	{
+		using var stream = await FileSystem.OpenAppPackageFileAsync("AboutAssets.txt");
+		using var reader = new StreamReader(stream);
+
+		var contents = reader.ReadToEnd();
+	}

src/Massenger.Client/Resources/Raw/firebase.android.json

@@ -0,0 +1,6 @@
+{
+  "applicationId": "",
+  "projectId": "",
+  "apiKey": "",
+  "senderId": ""
+}

src/Massenger.Client/Resources/Splash/splash.svg

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<svg width="456" height="456" viewBox="0 0 456 456" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xml:space="preserve" xmlns:serif="http://www.serif.com/" style="fill-rule:evenodd;clip-rule:evenodd;stroke-linejoin:round;stroke-miterlimit:2;">
+    <path d="m 105.50037,281.60863 c -2.70293,0 -5.00091,-0.90042 -6.893127,-2.70209 -1.892214,-1.84778 -2.837901,-4.04181 -2.837901,-6.58209 0,-2.58722 0.945687,-4.80389 2.837901,-6.65167 1.892217,-1.84778 4.190197,-2.77167 6.893127,-2.77167 2.74819,0 5.06798,0.92389 6.96019,2.77167 1.93749,1.84778 2.90581,4.06445 2.90581,6.65167 0,2.54028 -0.96832,4.73431 -2.90581,6.58209 -1.89221,1.80167 -4.212,2.70209 -6.96019,2.70209 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+    <path d="M 213.56111,280.08446 H 195.99044 L 149.69953,207.0544 c -1.17121,-1.84778 -2.14037,-3.76515 -2.90581,-5.75126 h -0.40578 c 0.36051,2.12528 0.54076,6.67515 0.54076,13.6496 v 65.13172 h -15.54349 v -99.36009 h 18.71925 l 44.7374,71.29798 c 1.89222,2.95695 3.1087,4.98917 3.64945,6.09751 h 0.26996 c -0.45021,-2.6325 -0.67573,-7.09015 -0.67573,-13.37293 v -64.02256 h 15.47557 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+    <path d="m 289.25134,280.08446 h -54.40052 v -99.36009 h 52.23835 v 13.99669 h -36.15411 v 28.13085 h 33.31621 v 13.9271 h -33.31621 v 29.37835 h 38.31628 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+    <path d="M 366.56466,194.72106 H 338.7222 v 85.3634 h -16.08423 v -85.3634 h -27.77455 v -13.99669 h 71.70124 z" style="fill:#ffffff;fill-rule:nonzero;stroke-width:0.838376" />
+</svg>

src/Massenger.Client/Resources/Styles/Colors.xaml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<ResourceDictionary
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">
+
+    <Color x:Key="Accent">#0F766E</Color>
+    <Color x:Key="AccentDeep">#115E59</Color>
+    <Color x:Key="AccentSoft">#D1FAE5</Color>
+    <Color x:Key="Surface">#FFFFFF</Color>
+    <Color x:Key="SurfaceMuted">#F8FAFC</Color>
+    <Color x:Key="Ink">#0F172A</Color>
+    <Color x:Key="InkMuted">#64748B</Color>
+    <Color x:Key="Danger">#B91C1C</Color>
+    <Color x:Key="Border">#CBD5E1</Color>
+
+    <SolidColorBrush x:Key="AccentBrush" Color="{StaticResource Accent}" />
+    <SolidColorBrush x:Key="SurfaceBrush" Color="{StaticResource Surface}" />
+    <SolidColorBrush x:Key="SurfaceMutedBrush" Color="{StaticResource SurfaceMuted}" />
+    <SolidColorBrush x:Key="BorderBrush" Color="{StaticResource Border}" />
+</ResourceDictionary>

src/Massenger.Client/Resources/Styles/Styles.xaml

@@ -0,0 +1,65 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<ResourceDictionary
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">
+
+    <Style TargetType="Page" ApplyToDerivedTypes="True">
+        <Setter Property="BackgroundColor" Value="{AppThemeBinding Light={StaticResource SurfaceMuted}, Dark=#020617}" />
+    </Style>
+
+    <Style TargetType="Border">
+        <Setter Property="BackgroundColor" Value="{AppThemeBinding Light={StaticResource Surface}, Dark=#0F172A}" />
+        <Setter Property="Stroke" Value="{AppThemeBinding Light={StaticResource Border}, Dark=#1E293B}" />
+        <Setter Property="StrokeThickness" Value="1" />
+    </Style>
+
+    <Style TargetType="Label">
+        <Setter Property="TextColor" Value="{AppThemeBinding Light={StaticResource Ink}, Dark=White}" />
+        <Setter Property="FontFamily" Value="OpenSansRegular" />
+    </Style>
+
+    <Style TargetType="Button">
+        <Setter Property="BackgroundColor" Value="{StaticResource Accent}" />
+        <Setter Property="TextColor" Value="White" />
+        <Setter Property="CornerRadius" Value="14" />
+        <Setter Property="Padding" Value="18,12" />
+        <Setter Property="FontFamily" Value="OpenSansSemibold" />
+    </Style>
+
+    <Style TargetType="Entry">
+        <Setter Property="BackgroundColor" Value="{AppThemeBinding Light=White, Dark=#0F172A}" />
+        <Setter Property="TextColor" Value="{AppThemeBinding Light={StaticResource Ink}, Dark=White}" />
+        <Setter Property="PlaceholderColor" Value="{StaticResource InkMuted}" />
+        <Setter Property="FontFamily" Value="OpenSansRegular" />
+    </Style>
+
+    <Style TargetType="Editor">
+        <Setter Property="BackgroundColor" Value="{AppThemeBinding Light=White, Dark=#0F172A}" />
+        <Setter Property="TextColor" Value="{AppThemeBinding Light={StaticResource Ink}, Dark=White}" />
+        <Setter Property="PlaceholderColor" Value="{StaticResource InkMuted}" />
+        <Setter Property="FontFamily" Value="OpenSansRegular" />
+    </Style>
+
+    <Style TargetType="CheckBox">
+        <Setter Property="Color" Value="{StaticResource Accent}" />
+    </Style>
+
+    <Style TargetType="Switch">
+        <Setter Property="OnColor" Value="{StaticResource AccentSoft}" />
+        <Setter Property="ThumbColor" Value="{StaticResource Accent}" />
+    </Style>
+
+    <Style TargetType="ActivityIndicator">
+        <Setter Property="Color" Value="{StaticResource Accent}" />
+    </Style>
+
+    <Style TargetType="Shell" ApplyToDerivedTypes="True">
+        <Setter Property="Shell.BackgroundColor" Value="{StaticResource Surface}" />
+        <Setter Property="Shell.ForegroundColor" Value="{StaticResource Ink}" />
+        <Setter Property="Shell.TitleColor" Value="{StaticResource Ink}" />
+        <Setter Property="Shell.TabBarBackgroundColor" Value="{StaticResource Surface}" />
+        <Setter Property="Shell.TabBarForegroundColor" Value="{StaticResource Accent}" />
+        <Setter Property="Shell.TabBarTitleColor" Value="{StaticResource Accent}" />
+        <Setter Property="Shell.TabBarUnselectedColor" Value="{StaticResource InkMuted}" />
+    </Style>
+</ResourceDictionary>

src/Massenger.Client/Services/ApiClient.cs

@@ -0,0 +1,348 @@
+using System.Net;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text;
+using System.Text.Json;
+using Microsoft.Maui.Storage;
+using Massenger.Shared;
+
+namespace Massenger.Client.Services;
+
+public sealed class ApiClient(ServerEndpointStore endpointStore, SessionService sessionService)
+{
+    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);
+    private readonly SemaphoreSlim _refreshLock = new(1, 1);
+
+    public Task<AuthSessionDto> LoginAsync(LoginRequest request, CancellationToken cancellationToken = default) =>
+        SendAsync<AuthSessionDto>(HttpMethod.Post, "api/auth/login", request, cancellationToken, requiresAuth: false);
+
+    public Task<AuthSessionDto> RegisterAsync(RegisterRequest request, CancellationToken cancellationToken = default) =>
+        SendAsync<AuthSessionDto>(HttpMethod.Post, "api/auth/register", request, cancellationToken, requiresAuth: false);
+
+    public Task<AuthSessionDto> RefreshAsync(string refreshToken, CancellationToken cancellationToken = default) =>
+        SendAsync<AuthSessionDto>(
+            HttpMethod.Post,
+            "api/auth/refresh",
+            new RefreshSessionRequest(refreshToken),
+            cancellationToken,
+            requiresAuth: false);
+
+    public Task LogoutAsync(CancellationToken cancellationToken = default) =>
+        SendAsync(HttpMethod.Post, "api/auth/logout", null, cancellationToken);
+
+    public Task<IReadOnlyList<PushDeviceDto>> GetPushDevicesAsync(CancellationToken cancellationToken = default) =>
+        SendAsync<IReadOnlyList<PushDeviceDto>>(HttpMethod.Get, "api/push/devices", null, cancellationToken);
+
+    public Task<PushDeviceDto> RegisterPushDeviceAsync(RegisterPushDeviceRequest request, CancellationToken cancellationToken = default) =>
+        SendAsync<PushDeviceDto>(HttpMethod.Post, "api/push/devices", request, cancellationToken);
+
+    public Task UnregisterPushDeviceAsync(string installationId, CancellationToken cancellationToken = default) =>
+        SendAsync(HttpMethod.Delete, $"api/push/devices/{Uri.EscapeDataString(installationId)}", null, cancellationToken);
+
+    public Task<UserSummaryDto> GetMeAsync(CancellationToken cancellationToken = default) =>
+        SendAsync<UserSummaryDto>(HttpMethod.Get, "api/users/me", null, cancellationToken);
+
+    public Task<IReadOnlyList<UserSummaryDto>> SearchUsersAsync(string query, CancellationToken cancellationToken = default) =>
+        SendAsync<IReadOnlyList<UserSummaryDto>>(HttpMethod.Get, $"api/users/search?q={Uri.EscapeDataString(query)}", null, cancellationToken);
+
+    public Task<IReadOnlyList<ChatSummaryDto>> GetChatsAsync(CancellationToken cancellationToken = default) =>
+        SendAsync<IReadOnlyList<ChatSummaryDto>>(HttpMethod.Get, "api/chats", null, cancellationToken);
+
+    public Task<ChatDetailsDto> GetChatAsync(Guid chatId, CancellationToken cancellationToken = default) =>
+        SendAsync<ChatDetailsDto>(HttpMethod.Get, $"api/chats/{chatId}", null, cancellationToken);
+
+    public Task<ChatDetailsDto> CreateDirectChatAsync(Guid userId, CancellationToken cancellationToken = default) =>
+        SendAsync<ChatDetailsDto>(HttpMethod.Post, "api/chats/direct", new CreateDirectChatRequest(userId), cancellationToken);
+
+    public Task<ChatDetailsDto> CreateGroupChatAsync(string title, IReadOnlyList<Guid> memberIds, CancellationToken cancellationToken = default) =>
+        SendAsync<ChatDetailsDto>(HttpMethod.Post, "api/chats/group", new CreateGroupChatRequest(title, memberIds), cancellationToken);
+
+    public Task<ChatDetailsDto> CreateChannelAsync(string title, IReadOnlyList<Guid> memberIds, CancellationToken cancellationToken = default) =>
+        SendAsync<ChatDetailsDto>(HttpMethod.Post, "api/chats/channel", new CreateChannelRequest(title, memberIds), cancellationToken);
+
+    public Task<MessageDto> SendMessageAsync(Guid chatId, string text, CancellationToken cancellationToken = default) =>
+        SendAsync<MessageDto>(HttpMethod.Post, $"api/chats/{chatId}/messages", new SendMessageRequest(text), cancellationToken);
+
+    public Task<MessageDto> UpdateMessageAsync(Guid chatId, Guid messageId, string text, CancellationToken cancellationToken = default) =>
+        SendAsync<MessageDto>(HttpMethod.Put, $"api/chats/{chatId}/messages/{messageId}", new UpdateMessageRequest(text), cancellationToken);
+
+    public Task<MessageDto> DeleteMessageAsync(Guid chatId, Guid messageId, CancellationToken cancellationToken = default) =>
+        SendAsync<MessageDto>(HttpMethod.Delete, $"api/chats/{chatId}/messages/{messageId}", null, cancellationToken);
+
+    public async Task<MessageDto> UploadAttachmentAsync(
+        Guid chatId,
+        string? text,
+        FileResult fileResult,
+        CancellationToken cancellationToken = default)
+    {
+        var token = await GetValidAccessTokenAsync(cancellationToken);
+        using var client = CreateClient();
+        using var response = await SendAttachmentInternalAsync(client, chatId, text, fileResult, token, cancellationToken);
+
+        if (response.StatusCode == HttpStatusCode.Unauthorized && sessionService.CurrentSession is not null)
+        {
+            response.Dispose();
+            token = await ForceRefreshAsync(cancellationToken);
+            using var retriedResponse = await SendAttachmentInternalAsync(client, chatId, text, fileResult, token, cancellationToken);
+            if (!retriedResponse.IsSuccessStatusCode)
+            {
+                throw await CreateApiExceptionAsync(retriedResponse, cancellationToken);
+            }
+
+            var retriedPayload = await retriedResponse.Content.ReadFromJsonAsync<MessageDto>(JsonOptions, cancellationToken);
+            return retriedPayload ?? throw new InvalidOperationException("Server returned an empty response.");
+        }
+
+        if (!response.IsSuccessStatusCode)
+        {
+            throw await CreateApiExceptionAsync(response, cancellationToken);
+        }
+
+        var payload = await response.Content.ReadFromJsonAsync<MessageDto>(JsonOptions, cancellationToken);
+        return payload ?? throw new InvalidOperationException("Server returned an empty response.");
+    }
+
+    public async Task<string> DownloadAttachmentAsync(AttachmentDto attachment, CancellationToken cancellationToken = default)
+    {
+        var token = await GetValidAccessTokenAsync(cancellationToken);
+        using var client = CreateClient();
+        using var response = await SendDownloadInternalAsync(client, attachment.DownloadPath, token, cancellationToken);
+
+        if (response.StatusCode == HttpStatusCode.Unauthorized && sessionService.CurrentSession is not null)
+        {
+            response.Dispose();
+            token = await ForceRefreshAsync(cancellationToken);
+            using var retriedResponse = await SendDownloadInternalAsync(client, attachment.DownloadPath, token, cancellationToken);
+            if (!retriedResponse.IsSuccessStatusCode)
+            {
+                throw await CreateApiExceptionAsync(retriedResponse, cancellationToken);
+            }
+
+            return await SaveAttachmentToCacheAsync(retriedResponse, attachment, cancellationToken);
+        }
+
+        if (!response.IsSuccessStatusCode)
+        {
+            throw await CreateApiExceptionAsync(response, cancellationToken);
+        }
+
+        return await SaveAttachmentToCacheAsync(response, attachment, cancellationToken);
+    }
+
+    private static async Task<string> SaveAttachmentToCacheAsync(
+        HttpResponseMessage response,
+        AttachmentDto attachment,
+        CancellationToken cancellationToken)
+    {
+        var safeName = $"{attachment.Id:N}_{Path.GetFileName(attachment.FileName)}";
+        var localPath = Path.Combine(FileSystem.CacheDirectory, safeName);
+
+        await using var responseStream = await response.Content.ReadAsStreamAsync(cancellationToken);
+        await using var fileStream = File.Create(localPath);
+        await responseStream.CopyToAsync(fileStream, cancellationToken);
+        return localPath;
+    }
+
+    public async Task<string?> GetValidAccessTokenAsync(CancellationToken cancellationToken = default)
+    {
+        var session = sessionService.CurrentSession;
+        if (session is null)
+        {
+            return null;
+        }
+
+        if (session.AccessTokenExpiresAt > DateTimeOffset.UtcNow.AddMinutes(1))
+        {
+            return session.AccessToken;
+        }
+
+        await _refreshLock.WaitAsync(cancellationToken);
+        try
+        {
+            session = sessionService.CurrentSession;
+            if (session is null)
+            {
+                return null;
+            }
+
+            if (session.AccessTokenExpiresAt > DateTimeOffset.UtcNow.AddMinutes(1))
+            {
+                return session.AccessToken;
+            }
+
+            var refreshed = await RefreshAsync(session.RefreshToken, cancellationToken);
+            await sessionService.RefreshAsync(refreshed);
+            return refreshed.AccessToken;
+        }
+        catch
+        {
+            await sessionService.SignOutAsync();
+            throw;
+        }
+        finally
+        {
+            _refreshLock.Release();
+        }
+    }
+
+    private async Task SendAsync(HttpMethod method, string relativeUrl, object? body, CancellationToken cancellationToken, bool requiresAuth = true)
+    {
+        using var response = await SendWithRetryAsync(method, relativeUrl, body, cancellationToken, requiresAuth);
+        if (!response.IsSuccessStatusCode)
+        {
+            throw await CreateApiExceptionAsync(response, cancellationToken);
+        }
+    }
+
+    private async Task<T> SendAsync<T>(HttpMethod method, string relativeUrl, object? body, CancellationToken cancellationToken, bool requiresAuth = true)
+    {
+        using var response = await SendWithRetryAsync(method, relativeUrl, body, cancellationToken, requiresAuth);
+        if (!response.IsSuccessStatusCode)
+        {
+            throw await CreateApiExceptionAsync(response, cancellationToken);
+        }
+
+        var payload = await response.Content.ReadFromJsonAsync<T>(JsonOptions, cancellationToken);
+        return payload ?? throw new InvalidOperationException("Server returned an empty response.");
+    }
+
+    private async Task<HttpResponseMessage> SendWithRetryAsync(
+        HttpMethod method,
+        string relativeUrl,
+        object? body,
+        CancellationToken cancellationToken,
+        bool requiresAuth)
+    {
+        using var client = CreateClient();
+        var token = requiresAuth ? await GetValidAccessTokenAsync(cancellationToken) : null;
+        var response = await SendOnceAsync(client, method, relativeUrl, body, token, cancellationToken);
+
+        if (response.StatusCode != HttpStatusCode.Unauthorized || !requiresAuth || sessionService.CurrentSession is null)
+        {
+            return response;
+        }
+
+        response.Dispose();
+        var refreshedToken = await ForceRefreshAsync(cancellationToken);
+        return await SendOnceAsync(client, method, relativeUrl, body, refreshedToken, cancellationToken);
+    }
+
+    private async Task<string?> ForceRefreshAsync(CancellationToken cancellationToken)
+    {
+        await _refreshLock.WaitAsync(cancellationToken);
+        try
+        {
+            var session = sessionService.CurrentSession;
+            if (session is null)
+            {
+                return null;
+            }
+
+            var refreshed = await RefreshAsync(session.RefreshToken, cancellationToken);
+            await sessionService.RefreshAsync(refreshed);
+            return refreshed.AccessToken;
+        }
+        catch
+        {
+            await sessionService.SignOutAsync();
+            throw;
+        }
+        finally
+        {
+            _refreshLock.Release();
+        }
+    }
+
+    private static async Task<HttpResponseMessage> SendOnceAsync(
+        HttpClient client,
+        HttpMethod method,
+        string relativeUrl,
+        object? body,
+        string? accessToken,
+        CancellationToken cancellationToken)
+    {
+        using var request = CreateRequest(method, relativeUrl, body, accessToken);
+        return await client.SendAsync(request, cancellationToken);
+    }
+
+    private static async Task<HttpResponseMessage> SendAttachmentInternalAsync(
+        HttpClient client,
+        Guid chatId,
+        string? text,
+        FileResult fileResult,
+        string? accessToken,
+        CancellationToken cancellationToken)
+    {
+        await using var fileStream = await fileResult.OpenReadAsync();
+        using var request = new HttpRequestMessage(HttpMethod.Post, $"api/chats/{chatId}/attachments");
+        if (!string.IsNullOrWhiteSpace(accessToken))
+        {
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
+        }
+
+        using var content = new MultipartFormDataContent();
+        if (!string.IsNullOrWhiteSpace(text))
+        {
+            content.Add(new StringContent(text), "text");
+        }
+
+        var streamContent = new StreamContent(fileStream);
+        streamContent.Headers.ContentType = new MediaTypeHeaderValue(
+            string.IsNullOrWhiteSpace(fileResult.ContentType) ? "application/octet-stream" : fileResult.ContentType);
+        content.Add(streamContent, "file", fileResult.FileName);
+        request.Content = content;
+
+        return await client.SendAsync(request, cancellationToken);
+    }
+
+    private static async Task<HttpResponseMessage> SendDownloadInternalAsync(
+        HttpClient client,
+        string downloadPath,
+        string? accessToken,
+        CancellationToken cancellationToken)
+    {
+        using var request = new HttpRequestMessage(HttpMethod.Get, downloadPath.TrimStart('/'));
+        if (!string.IsNullOrWhiteSpace(accessToken))
+        {
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
+        }
+
+        return await client.SendAsync(request, cancellationToken);
+    }
+
+    private HttpClient CreateClient() =>
+        new()
+        {
+            BaseAddress = new Uri($"{endpointStore.GetBaseUrl().TrimEnd('/')}/")
+        };
+
+    private static HttpRequestMessage CreateRequest(HttpMethod method, string relativeUrl, object? body, string? accessToken)
+    {
+        var request = new HttpRequestMessage(method, relativeUrl);
+        if (!string.IsNullOrWhiteSpace(accessToken))
+        {
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
+        }
+
+        if (body is null)
+        {
+            return request;
+        }
+
+        request.Content = new StringContent(
+            JsonSerializer.Serialize(body, JsonOptions),
+            Encoding.UTF8,
+            "application/json");
+
+        return request;
+    }
+
+    private static async Task<Exception> CreateApiExceptionAsync(HttpResponseMessage response, CancellationToken cancellationToken)
+    {
+        var content = await response.Content.ReadAsStringAsync(cancellationToken);
+        return new InvalidOperationException(
+            string.IsNullOrWhiteSpace(content)
+                ? $"Request failed with status {(int)response.StatusCode}."
+                : content);
+    }
+}

src/Massenger.Client/Services/IPushRegistrationService.cs

@@ -0,0 +1,10 @@
+namespace Massenger.Client.Services;
+
+public interface IPushRegistrationService
+{
+    Task InitializeAsync(CancellationToken cancellationToken = default);
+
+    Task RegisterCurrentDeviceAsync(CancellationToken cancellationToken = default);
+
+    Task UnregisterCurrentDeviceAsync(CancellationToken cancellationToken = default);
+}

src/Massenger.Client/Services/NoOpPushRegistrationService.cs

@@ -0,0 +1,10 @@
+namespace Massenger.Client.Services;
+
+public sealed class NoOpPushRegistrationService : IPushRegistrationService
+{
+    public Task InitializeAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
+
+    public Task RegisterCurrentDeviceAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
+
+    public Task UnregisterCurrentDeviceAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
+}

src/Massenger.Client/Services/NotificationActivationService.cs

@@ -0,0 +1,37 @@
+namespace Massenger.Client.Services;
+
+public sealed class NotificationActivationService
+{
+    private readonly object _sync = new();
+    private Guid? _pendingChatId;
+
+    public event EventHandler<Guid>? ChatRequested;
+
+    public void SetPendingChat(Guid chatId)
+    {
+        lock (_sync)
+        {
+            _pendingChatId = chatId;
+        }
+
+        ChatRequested?.Invoke(this, chatId);
+    }
+
+    public Guid? ConsumePendingChat()
+    {
+        lock (_sync)
+        {
+            var chatId = _pendingChatId;
+            _pendingChatId = null;
+            return chatId;
+        }
+    }
+
+    public void RestorePendingChat(Guid chatId)
+    {
+        lock (_sync)
+        {
+            _pendingChatId = chatId;
+        }
+    }
+}

src/Massenger.Client/Services/RealtimeService.cs

@@ -0,0 +1,100 @@
+using Microsoft.AspNetCore.SignalR.Client;
+using Massenger.Shared;
+
+namespace Massenger.Client.Services;
+
+public sealed class RealtimeService(ServerEndpointStore endpointStore, SessionService sessionService, ApiClient apiClient)
+{
+    private HubConnection? _connection;
+
+    public event EventHandler<MessageDto>? MessageReceived;
+
+    public event EventHandler<MessageDto>? MessageUpdated;
+
+    public event EventHandler<ChatSummaryDto>? ChatCreated;
+
+    public event EventHandler? ChatsChanged;
+
+    public event EventHandler<string>? ConnectionStateChanged;
+
+    public string StatusText { get; private set; } = "offline";
+
+    public async Task ConnectAsync()
+    {
+        if (!sessionService.IsAuthenticated)
+        {
+            return;
+        }
+
+        if (_connection is not null && _connection.State is HubConnectionState.Connected or HubConnectionState.Connecting)
+        {
+            return;
+        }
+
+        if (_connection is null)
+        {
+            _connection = new HubConnectionBuilder()
+                .WithUrl(endpointStore.GetHubUrl(), options =>
+                {
+                    options.AccessTokenProvider = () => apiClient.GetValidAccessTokenAsync();
+                })
+                .WithAutomaticReconnect()
+                .Build();
+
+            _connection.On<MessageDto>("MessageCreated", message => MessageReceived?.Invoke(this, message));
+            _connection.On<MessageDto>("MessageUpdated", message => MessageUpdated?.Invoke(this, message));
+            _connection.On<ChatSummaryDto>("ChatCreated", chat => ChatCreated?.Invoke(this, chat));
+            _connection.On("ChatsChanged", () => ChatsChanged?.Invoke(this, EventArgs.Empty));
+
+            _connection.Reconnecting += error =>
+            {
+                UpdateStatus("reconnecting");
+                return Task.CompletedTask;
+            };
+
+            _connection.Reconnected += connectionId =>
+            {
+                UpdateStatus("online");
+                return Task.CompletedTask;
+            };
+
+            _connection.Closed += error =>
+            {
+                UpdateStatus("offline");
+                return Task.CompletedTask;
+            };
+        }
+
+        await _connection.StartAsync();
+        UpdateStatus("online");
+    }
+
+    public async Task DisconnectAsync()
+    {
+        if (_connection is null)
+        {
+            UpdateStatus("offline");
+            return;
+        }
+
+        if (_connection.State != HubConnectionState.Disconnected)
+        {
+            await _connection.StopAsync();
+        }
+
+        UpdateStatus("offline");
+    }
+
+    public async Task ReconnectAsync()
+    {
+        await DisconnectAsync();
+        _connection = null;
+        await ConnectAsync();
+    }
+
+    private void UpdateStatus(string status)
+    {
+        StatusText = status;
+        ConnectionStateChanged?.Invoke(this, status);
+    }
+}

src/Massenger.Client/Services/ServerEndpointStore.cs

@@ -0,0 +1,41 @@
+namespace Massenger.Client.Services;
+
+public sealed class ServerEndpointStore
+{
+    private const string PreferenceKey = "server_url";
+
+    public string GetBaseUrl()
+    {
+        var stored = Preferences.Default.Get(PreferenceKey, string.Empty);
+        return string.IsNullOrWhiteSpace(stored) ? GetDefaultUrl() : stored;
+    }
+
+    public void SetBaseUrl(string url)
+    {
+        Preferences.Default.Set(PreferenceKey, Normalize(url));
+    }
+
+    public string GetHubUrl() => $"{GetBaseUrl().TrimEnd('/')}/hubs/messenger";
+
+    public string Normalize(string url)
+    {
+        var trimmed = url.Trim().TrimEnd('/');
+        if (!trimmed.StartsWith("http://", StringComparison.OrdinalIgnoreCase) &&
+            !trimmed.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
+        {
+            trimmed = $"http://{trimmed}";
+        }
+
+        return trimmed;
+    }
+
+    private static string GetDefaultUrl()
+    {
+        if (DeviceInfo.Platform == DevicePlatform.Android)
+        {
+            return "http://10.0.2.2:5099";
+        }
+
+        return "http://localhost:5099";
+    }
+}

src/Massenger.Client/Services/ServiceHelper.cs

@@ -0,0 +1,19 @@
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Massenger.Client.Services;
+
+public static class ServiceHelper
+{
+    public static IServiceProvider Services { get; private set; } = null!;
+
+    public static void Initialize(IServiceProvider services)
+    {
+        Services = services;
+    }
+
+    public static T GetRequiredService<T>() where T : notnull =>
+        Services.GetRequiredService<T>();
+
+    public static T? GetService<T>() where T : class =>
+        Services.GetService<T>();
+}

src/Massenger.Client/Services/SessionService.cs

@@ -0,0 +1,88 @@
+using System.Text.Json;
+using Massenger.Client.Models;
+using Massenger.Shared;
+
+namespace Massenger.Client.Services;
+
+public sealed class SessionService
+{
+    private const string SecureSessionKey = "auth_session";
+
+    public event EventHandler? SessionChanged;
+
+    public ClientSession? CurrentSession { get; private set; }
+
+    public bool IsAuthenticated => CurrentSession is not null;
+
+    public async Task RestoreAsync()
+    {
+        if (CurrentSession is not null)
+        {
+            return;
+        }
+
+        try
+        {
+            var sessionJson = await SecureStorage.Default.GetAsync(SecureSessionKey);
+            if (string.IsNullOrWhiteSpace(sessionJson))
+            {
+                return;
+            }
+
+            CurrentSession = JsonSerializer.Deserialize<ClientSession>(sessionJson);
+        }
+        catch
+        {
+            CurrentSession = null;
+        }
+    }
+
+    public Task SignInAsync(AuthSessionDto session) => SetSessionAsync(session, notify: true);
+
+    public Task RefreshAsync(AuthSessionDto session) => SetSessionAsync(session, notify: false);
+
+    public async Task UpdateCurrentUserAsync(UserSummaryDto user)
+    {
+        if (CurrentSession is null)
+        {
+            return;
+        }
+
+        CurrentSession = CurrentSession with { User = user };
+        await PersistAsync();
+    }
+
+    public async Task SignOutAsync()
+    {
+        CurrentSession = null;
+        SecureStorage.Default.Remove(SecureSessionKey);
+        SessionChanged?.Invoke(this, EventArgs.Empty);
+        await Task.CompletedTask;
+    }
+
+    private async Task SetSessionAsync(AuthSessionDto session, bool notify)
+    {
+        CurrentSession = new ClientSession(
+            session.AccessToken,
+            session.RefreshToken,
+            session.AccessTokenExpiresAt,
+            session.User);
+
+        await PersistAsync();
+        if (notify)
+        {
+            SessionChanged?.Invoke(this, EventArgs.Empty);
+        }
+    }
+
+    private Task PersistAsync()
+    {
+        if (CurrentSession is null)
+        {
+            return Task.CompletedTask;
+        }
+
+        var payload = JsonSerializer.Serialize(CurrentSession);
+        return SecureStorage.Default.SetAsync(SecureSessionKey, payload);
+    }
+}

src/Massenger.Client/ViewModels/BaseViewModel.cs

@@ -0,0 +1,42 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace Massenger.Client.ViewModels;
+
+public partial class BaseViewModel : ObservableObject
+{
+    [ObservableProperty]
+    private bool isBusy;
+
+    [ObservableProperty]
+    private string? errorMessage;
+
+    public bool HasError => !string.IsNullOrWhiteSpace(ErrorMessage);
+
+    partial void OnErrorMessageChanged(string? value)
+    {
+        OnPropertyChanged(nameof(HasError));
+    }
+
+    protected async Task RunBusyAsync(Func<Task> action)
+    {
+        if (IsBusy)
+        {
+            return;
+        }
+
+        try
+        {
+            ErrorMessage = null;
+            IsBusy = true;
+            await action();
+        }
+        catch (Exception ex)
+        {
+            ErrorMessage = ex.Message;
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
+}

src/Massenger.Client/ViewModels/ChatViewModel.cs

@@ -0,0 +1,316 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Massenger.Client.Models;
+using Massenger.Client.Services;
+using Massenger.Shared;
+
+namespace Massenger.Client.ViewModels;
+
+public partial class ChatViewModel(
+    ApiClient apiClient,
+    RealtimeService realtimeService,
+    SessionService sessionService) : BaseViewModel
+{
+    private PendingAttachmentItem? _pendingAttachment;
+    private ChatMessageItem? _editingMessage;
+
+    public ObservableCollection<ChatMessageItem> Messages { get; } = [];
+
+    [ObservableProperty]
+    private Guid currentChatId;
+
+    [ObservableProperty]
+    private string title = "Conversation";
+
+    [ObservableProperty]
+    private string subtitle = string.Empty;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(SendMessageCommand))]
+    private string draftText = string.Empty;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(SendMessageCommand))]
+    private bool hasPendingAttachment;
+
+    [ObservableProperty]
+    private string pendingAttachmentName = string.Empty;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(SendMessageCommand))]
+    private bool canSendMessages = true;
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(SendMessageCommand))]
+    private bool isEditingMessage;
+
+    [ObservableProperty]
+    private string editingMessageBanner = string.Empty;
+
+    public bool ShowComposer => CanSendMessages;
+
+    public bool ShowReadOnlyBanner => !CanSendMessages;
+
+    partial void OnCanSendMessagesChanged(bool value)
+    {
+        OnPropertyChanged(nameof(ShowComposer));
+        OnPropertyChanged(nameof(ShowReadOnlyBanner));
+    }
+
+    public void AttachRealtime()
+    {
+        realtimeService.MessageReceived -= OnMessageReceived;
+        realtimeService.MessageUpdated -= OnMessageUpdated;
+        realtimeService.MessageReceived += OnMessageReceived;
+        realtimeService.MessageUpdated += OnMessageUpdated;
+    }
+
+    public void DetachRealtime()
+    {
+        realtimeService.MessageReceived -= OnMessageReceived;
+        realtimeService.MessageUpdated -= OnMessageUpdated;
+    }
+
+    public async Task LoadAsync(Guid chatId)
+    {
+        CurrentChatId = chatId;
+        await RunBusyAsync(async () =>
+        {
+            var chat = await apiClient.GetChatAsync(chatId);
+            var currentUserId = sessionService.CurrentSession?.User.Id ?? Guid.Empty;
+
+            MainThread.BeginInvokeOnMainThread(() =>
+            {
+                Title = chat.Title;
+                Subtitle = BuildSubtitle(chat);
+                CanSendMessages = chat.CanSendMessages;
+                CancelEditMessage();
+                ClearPendingAttachment();
+                Messages.Clear();
+                foreach (var message in chat.Messages)
+                {
+                    Messages.Add(new ChatMessageItem(message, currentUserId));
+                }
+            });
+        });
+    }
+
+    private bool CanSendMessage() =>
+        !IsBusy &&
+        CurrentChatId != Guid.Empty &&
+        CanSendMessages &&
+        (IsEditingMessage
+            ? !string.IsNullOrWhiteSpace(DraftText) || _editingMessage?.HasAttachments == true
+            : !string.IsNullOrWhiteSpace(DraftText) || HasPendingAttachment);
+
+    [RelayCommand(CanExecute = nameof(CanSendMessage))]
+    private Task SendMessageAsync() =>
+        RunBusyAsync(async () =>
+        {
+            MessageDto message;
+            if (IsEditingMessage && _editingMessage is not null)
+            {
+                message = await apiClient.UpdateMessageAsync(CurrentChatId, _editingMessage.Id, DraftText);
+                CancelEditMessage();
+            }
+            else if (_pendingAttachment is not null)
+            {
+                message = await apiClient.UploadAttachmentAsync(CurrentChatId, DraftText, _pendingAttachment.File);
+                ClearPendingAttachment();
+                DraftText = string.Empty;
+            }
+            else
+            {
+                message = await apiClient.SendMessageAsync(CurrentChatId, DraftText);
+                DraftText = string.Empty;
+            }
+
+            ReplaceOrInsertMessage(message);
+        });
+
+    [RelayCommand]
+    private Task PickAttachmentAsync() =>
+        PickPendingAttachmentAsync(requireVoiceFile: false);
+
+    [RelayCommand]
+    private Task PickVoiceNoteAsync() =>
+        PickPendingAttachmentAsync(requireVoiceFile: true);
+
+    [RelayCommand]
+    private void BeginEditMessage(ChatMessageItem? message)
+    {
+        if (message is null || !message.CanManage)
+        {
+            return;
+        }
+
+        ClearPendingAttachment();
+        _editingMessage = message;
+        IsEditingMessage = true;
+        EditingMessageBanner = $"Editing message from {message.Timestamp}";
+        DraftText = message.RawText;
+    }
+
+    [RelayCommand]
+    private void CancelEditMessage()
+    {
+        _editingMessage = null;
+        IsEditingMessage = false;
+        EditingMessageBanner = string.Empty;
+        DraftText = string.Empty;
+    }
+
+    [RelayCommand]
+    private Task DeleteMessageAsync(ChatMessageItem? message) =>
+        RunBusyAsync(async () =>
+        {
+            if (message is null || !message.CanManage)
+            {
+                return;
+            }
+
+            var confirmed = await Shell.Current.DisplayAlertAsync(
+                "Delete message",
+                "Delete this message for all channel/chat members?",
+                "Delete",
+                "Cancel");
+
+            if (!confirmed)
+            {
+                return;
+            }
+
+            var updated = await apiClient.DeleteMessageAsync(CurrentChatId, message.Id);
+            if (_editingMessage?.Id == message.Id)
+            {
+                CancelEditMessage();
+            }
+
+            ReplaceOrInsertMessage(updated);
+        });
+
+    [RelayCommand]
+    private Task PickPendingAttachmentAsync(bool requireVoiceFile) =>
+        RunBusyAsync(async () =>
+        {
+            var picked = await FilePicker.Default.PickAsync();
+            if (picked is null)
+            {
+                return;
+            }
+
+            var pending = PendingAttachmentItem.Create(picked);
+            if (requireVoiceFile && pending.Kind != AttachmentKind.VoiceNote)
+            {
+                throw new InvalidOperationException("Selected file is not recognized as audio.");
+            }
+
+            CancelEditMessage();
+            _pendingAttachment = requireVoiceFile
+                ? new PendingAttachmentItem(picked, AttachmentKind.VoiceNote)
+                : pending;
+            PendingAttachmentName = _pendingAttachment.DisplayName;
+            HasPendingAttachment = true;
+        });
+
+    [RelayCommand]
+    private void RemovePendingAttachment()
+    {
+        ClearPendingAttachment();
+    }
+
+    [RelayCommand]
+    private Task OpenAttachmentAsync(ChatAttachmentItem? attachment) =>
+        RunBusyAsync(async () =>
+        {
+            if (attachment is null)
+            {
+                return;
+            }
+
+            var localPath = await apiClient.DownloadAttachmentAsync(
+                new AttachmentDto(
+                    attachment.Id,
+                    attachment.FileName,
+                    attachment.ContentType,
+                    attachment.FileSizeBytes,
+                    attachment.DownloadPath,
+                    attachment.Kind));
+
+            await Launcher.Default.OpenAsync(
+                new OpenFileRequest(
+                    attachment.FileName,
+                    new ReadOnlyFile(localPath)));
+        });
+
+    private void OnMessageReceived(object? sender, MessageDto message)
+    {
+        if (message.ChatId != CurrentChatId)
+        {
+            return;
+        }
+
+        MainThread.BeginInvokeOnMainThread(() => ReplaceOrInsertMessage(message));
+    }
+
+    private void OnMessageUpdated(object? sender, MessageDto message)
+    {
+        if (message.ChatId != CurrentChatId)
+        {
+            return;
+        }
+
+        MainThread.BeginInvokeOnMainThread(() =>
+        {
+            if (_editingMessage?.Id == message.Id && message.DeletedAt is not null)
+            {
+                CancelEditMessage();
+            }
+
+            ReplaceOrInsertMessage(message);
+        });
+    }
+
+    private void ReplaceOrInsertMessage(MessageDto message)
+    {
+        var currentUserId = sessionService.CurrentSession?.User.Id ?? Guid.Empty;
+        var item = new ChatMessageItem(message, currentUserId);
+        var index = Messages
+            .Select((value, idx) => new { value, idx })
+            .FirstOrDefault(x => x.value.Id == message.Id)
+            ?.idx;
+
+        if (index is int existingIndex)
+        {
+            Messages[existingIndex] = item;
+        }
+        else
+        {
+            Messages.Add(item);
+        }
+
+        var ordered = Messages.OrderBy(x => x.SentAt).ToList();
+        Messages.Clear();
+        foreach (var orderedItem in ordered)
+        {
+            Messages.Add(orderedItem);
+        }
+    }
+
+    private static string BuildSubtitle(ChatDetailsDto chat) =>
+        chat.Type switch
+        {
+            ChatType.Channel => chat.CanSendMessages
+                ? $"{chat.Participants.Count} members | you can publish"
+                : $"{chat.Participants.Count} members | read-only channel",
+            _ => $"{chat.Participants.Count} members"
+        };
+
+    private void ClearPendingAttachment()
+    {
+        _pendingAttachment = null;
+        PendingAttachmentName = string.Empty;
+        HasPendingAttachment = false;
+    }
+}

src/Massenger.Client/ViewModels/ChatsViewModel.cs

@@ -0,0 +1,77 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Massenger.Client.Pages;
+using Massenger.Client.Services;
+using Massenger.Shared;
+
+namespace Massenger.Client.ViewModels;
+
+public partial class ChatsViewModel(ApiClient apiClient, RealtimeService realtimeService) : BaseViewModel
+{
+    public ObservableCollection<ChatSummaryDto> Chats { get; } = [];
+
+    [ObservableProperty]
+    private ChatSummaryDto? selectedChat;
+
+    public string EmptyState => Chats.Count == 0 ? "No chats yet. Open Discover to start a dialog, group or channel." : string.Empty;
+
+    [RelayCommand]
+    public async Task LoadAsync()
+    {
+        await RunBusyAsync(async () =>
+        {
+            var chats = await apiClient.GetChatsAsync();
+            MainThread.BeginInvokeOnMainThread(() =>
+            {
+                Chats.Clear();
+                foreach (var chat in chats)
+                {
+                    Chats.Add(chat);
+                }
+
+                OnPropertyChanged(nameof(EmptyState));
+            });
+        });
+    }
+
+    [RelayCommand]
+    public async Task OpenChatAsync(ChatSummaryDto? chat)
+    {
+        if (chat is null)
+        {
+            return;
+        }
+
+        SelectedChat = null;
+        await Shell.Current.GoToAsync($"{nameof(ChatPage)}?chatId={chat.Id}");
+    }
+
+    public void AttachRealtime()
+    {
+        realtimeService.MessageReceived -= OnRealtimeChanged;
+        realtimeService.MessageUpdated -= OnRealtimeChanged;
+        realtimeService.ChatCreated -= OnChatCreated;
+        realtimeService.ChatsChanged -= OnRealtimeChanged;
+
+        realtimeService.MessageReceived += OnRealtimeChanged;
+        realtimeService.MessageUpdated += OnRealtimeChanged;
+        realtimeService.ChatCreated += OnChatCreated;
+        realtimeService.ChatsChanged += OnRealtimeChanged;
+    }
+
+    private void OnChatCreated(object? sender, ChatSummaryDto e)
+    {
+        MainThread.BeginInvokeOnMainThread(() => _ = LoadAsync());
+    }
+
+    private void OnRealtimeChanged(object? sender, EventArgs e)
+    {
+        MainThread.BeginInvokeOnMainThread(() => _ = LoadAsync());
+    }
+
+    private void OnRealtimeChanged(object? sender, MessageDto e)
+    {
+        MainThread.BeginInvokeOnMainThread(() => _ = LoadAsync());
+    }
+}

src/Massenger.Client/ViewModels/DiscoverViewModel.cs

@@ -0,0 +1,118 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Massenger.Client.Models;
+using Massenger.Client.Pages;
+using Massenger.Client.Services;
+
+namespace Massenger.Client.ViewModels;
+
+public partial class DiscoverViewModel(ApiClient apiClient) : BaseViewModel
+{
+    public ObservableCollection<DiscoverUserItem> Results { get; } = [];
+
+    [ObservableProperty]
+    private string query = string.Empty;
+
+    [ObservableProperty]
+    private string groupTitle = string.Empty;
+
+    [ObservableProperty]
+    private string channelTitle = string.Empty;
+
+    public int SelectedCount => Results.Count(x => x.IsSelected);
+
+    [RelayCommand]
+    public Task SearchAsync() =>
+        RunBusyAsync(async () =>
+        {
+            var users = await apiClient.SearchUsersAsync(Query);
+            MainThread.BeginInvokeOnMainThread(() =>
+            {
+                Results.Clear();
+                foreach (var user in users)
+                {
+                    var item = new DiscoverUserItem(user);
+                    item.PropertyChanged += (_, args) =>
+                    {
+                        if (args.PropertyName == nameof(DiscoverUserItem.IsSelected))
+                        {
+                            OnPropertyChanged(nameof(SelectedCount));
+                        }
+                    };
+
+                    Results.Add(item);
+                }
+
+                OnPropertyChanged(nameof(SelectedCount));
+            });
+        });
+
+    [RelayCommand]
+    public async Task StartDirectChatAsync(DiscoverUserItem? user)
+    {
+        if (user is null)
+        {
+            return;
+        }
+
+        await RunBusyAsync(async () =>
+        {
+            var chat = await apiClient.CreateDirectChatAsync(user.Id);
+            await Shell.Current.GoToAsync($"{nameof(ChatPage)}?chatId={chat.Id}");
+        });
+    }
+
+    [RelayCommand]
+    public Task CreateGroupAsync() =>
+        RunBusyAsync(async () =>
+        {
+            var members = GetSelectedMembers();
+
+            if (members.Count < 2)
+            {
+                throw new InvalidOperationException("Select at least two users for a group.");
+            }
+
+            if (string.IsNullOrWhiteSpace(GroupTitle))
+            {
+                throw new InvalidOperationException("Group title is required.");
+            }
+
+            var chat = await apiClient.CreateGroupChatAsync(GroupTitle, members);
+            GroupTitle = string.Empty;
+            ClearSelection();
+            await Shell.Current.GoToAsync($"{nameof(ChatPage)}?chatId={chat.Id}");
+        });
+
+    [RelayCommand]
+    public Task CreateChannelAsync() =>
+        RunBusyAsync(async () =>
+        {
+            if (string.IsNullOrWhiteSpace(ChannelTitle))
+            {
+                throw new InvalidOperationException("Channel title is required.");
+            }
+
+            var chat = await apiClient.CreateChannelAsync(ChannelTitle, GetSelectedMembers());
+            ChannelTitle = string.Empty;
+            ClearSelection();
+            await Shell.Current.GoToAsync($"{nameof(ChatPage)}?chatId={chat.Id}");
+        });
+
+    private List<Guid> GetSelectedMembers() =>
+        Results
+            .Where(x => x.IsSelected)
+            .Select(x => x.Id)
+            .ToList();
+
+    private void ClearSelection()
+    {
+        foreach (var item in Results)
+        {
+            item.IsSelected = false;
+        }
+
+        OnPropertyChanged(nameof(SelectedCount));
+    }
+}

src/Massenger.Client/ViewModels/LoginViewModel.cs

@@ -0,0 +1,58 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Massenger.Client.Services;
+using Massenger.Shared;
+
+namespace Massenger.Client.ViewModels;
+
+public partial class LoginViewModel(
+    ApiClient apiClient,
+    SessionService sessionService,
+    ServerEndpointStore endpointStore) : BaseViewModel
+{
+    [ObservableProperty]
+    private string username = "alice";
+
+    [ObservableProperty]
+    private string displayName = "Alice Carter";
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(AuthenticateCommand))]
+    private string password = "demo123";
+
+    [ObservableProperty]
+    [NotifyCanExecuteChangedFor(nameof(AuthenticateCommand))]
+    private string serverUrl = endpointStore.GetBaseUrl();
+
+    [ObservableProperty]
+    private bool isRegisterMode;
+
+    public string PageTitle => IsRegisterMode ? "Create your account" : "Sign in to Massenger";
+
+    public string PrimaryActionText => IsRegisterMode ? "Create account" : "Sign in";
+
+    partial void OnIsRegisterModeChanged(bool value)
+    {
+        OnPropertyChanged(nameof(PageTitle));
+        OnPropertyChanged(nameof(PrimaryActionText));
+    }
+
+    private bool CanAuthenticate() =>
+        !IsBusy &&
+        !string.IsNullOrWhiteSpace(Username) &&
+        !string.IsNullOrWhiteSpace(Password) &&
+        !string.IsNullOrWhiteSpace(ServerUrl);
+
+    [RelayCommand(CanExecute = nameof(CanAuthenticate))]
+    private Task AuthenticateAsync() =>
+        RunBusyAsync(async () =>
+        {
+            endpointStore.SetBaseUrl(ServerUrl);
+
+            AuthSessionDto session = IsRegisterMode
+                ? await apiClient.RegisterAsync(new RegisterRequest(Username, DisplayName, Password))
+                : await apiClient.LoginAsync(new LoginRequest(Username, Password));
+
+            await sessionService.SignInAsync(session);
+        });
+}

src/Massenger.Client/ViewModels/ProfileViewModel.cs

@@ -0,0 +1,74 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Massenger.Client.Services;
+
+namespace Massenger.Client.ViewModels;
+
+public partial class ProfileViewModel(
+    ApiClient apiClient,
+    SessionService sessionService,
+    ServerEndpointStore endpointStore,
+    RealtimeService realtimeService,
+    IPushRegistrationService pushRegistrationService) : BaseViewModel
+{
+    [ObservableProperty]
+    private string displayName = string.Empty;
+
+    [ObservableProperty]
+    private string username = string.Empty;
+
+    [ObservableProperty]
+    private string serverUrl = endpointStore.GetBaseUrl();
+
+    [ObservableProperty]
+    private string connectionStatus = realtimeService.StatusText;
+
+    public async Task LoadAsync()
+    {
+        ServerUrl = endpointStore.GetBaseUrl();
+        ConnectionStatus = realtimeService.StatusText;
+
+        var user = sessionService.CurrentSession?.User;
+        if (user is not null)
+        {
+            DisplayName = user.DisplayName;
+            Username = $"@{user.Username}";
+        }
+    }
+
+    [RelayCommand]
+    private Task SaveServerAsync() =>
+        RunBusyAsync(async () =>
+        {
+            endpointStore.SetBaseUrl(ServerUrl);
+            await realtimeService.ReconnectAsync();
+            var user = await apiClient.GetMeAsync();
+            await sessionService.UpdateCurrentUserAsync(user);
+            await LoadAsync();
+        });
+
+    [RelayCommand]
+    private Task RefreshProfileAsync() =>
+        RunBusyAsync(async () =>
+        {
+            var user = await apiClient.GetMeAsync();
+            await sessionService.UpdateCurrentUserAsync(user);
+            await LoadAsync();
+        });
+
+    [RelayCommand]
+    private async Task LogoutAsync()
+    {
+        try
+        {
+            await pushRegistrationService.UnregisterCurrentDeviceAsync();
+            await apiClient.LogoutAsync();
+        }
+        catch
+        {
+            // Local sign-out remains valid even if the server is offline.
+        }
+
+        await sessionService.SignOutAsync();
+    }
+}

src/Massenger.Server/Controllers/AuthController.cs

@@ -0,0 +1,104 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Identity;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+using Massenger.Server.Infrastructure;
+using Massenger.Server.Infrastructure.Auth;
+using Massenger.Shared;
+
+namespace Massenger.Server.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public sealed class AuthController(
+    MassengerDbContext dbContext,
+    TokenService tokenService,
+    PresenceTracker presenceTracker) : ControllerBase
+{
+    private readonly PasswordHasher<User> _passwordHasher = new();
+
+    [HttpPost("register")]
+    [AllowAnonymous]
+    public async Task<ActionResult<AuthSessionDto>> Register(RegisterRequest request, CancellationToken cancellationToken)
+    {
+        var username = request.Username.Trim();
+        var displayName = request.DisplayName.Trim();
+
+        if (string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(displayName) || request.Password.Length < 6)
+        {
+            return ValidationProblem("Username, display name and a password of at least 6 characters are required.");
+        }
+
+        var normalizedUsername = username.ToUpperInvariant();
+        if (await dbContext.Users.AnyAsync(x => x.NormalizedUsername == normalizedUsername, cancellationToken))
+        {
+            return Conflict("Username is already taken.");
+        }
+
+        var user = new User
+        {
+            Username = username,
+            NormalizedUsername = normalizedUsername,
+            DisplayName = displayName
+        };
+
+        user.PasswordHash = _passwordHasher.HashPassword(user, request.Password);
+        dbContext.Users.Add(user);
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var session = await tokenService.CreateSessionAsync(user, cancellationToken);
+        return Ok(session with { User = user.ToDto(presenceTracker) });
+    }
+
+    [HttpPost("login")]
+    [AllowAnonymous]
+    public async Task<ActionResult<AuthSessionDto>> Login(LoginRequest request, CancellationToken cancellationToken)
+    {
+        var normalizedUsername = request.Username.Trim().ToUpperInvariant();
+        var user = await dbContext.Users.SingleOrDefaultAsync(
+            x => x.NormalizedUsername == normalizedUsername,
+            cancellationToken);
+
+        if (user is null)
+        {
+            return Unauthorized("Invalid username or password.");
+        }
+
+        var verification = _passwordHasher.VerifyHashedPassword(user, user.PasswordHash, request.Password);
+        if (verification == PasswordVerificationResult.Failed)
+        {
+            return Unauthorized("Invalid username or password.");
+        }
+
+        var session = await tokenService.CreateSessionAsync(user, cancellationToken);
+        return Ok(session with { User = user.ToDto(presenceTracker) });
+    }
+
+    [HttpPost("refresh")]
+    [AllowAnonymous]
+    public async Task<ActionResult<AuthSessionDto>> Refresh(RefreshSessionRequest request, CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(request.RefreshToken))
+        {
+            return Unauthorized();
+        }
+
+        var session = await tokenService.RefreshSessionAsync(request.RefreshToken, cancellationToken);
+        if (session is null)
+        {
+            return Unauthorized();
+        }
+
+        return Ok(session with { User = session.User with { IsOnline = presenceTracker.IsOnline(session.User.Id) } });
+    }
+
+    [HttpPost("logout")]
+    [Authorize]
+    public async Task<IActionResult> Logout(CancellationToken cancellationToken)
+    {
+        await tokenService.RevokeSessionAsync(User.GetRequiredSessionId(), cancellationToken);
+        return NoContent();
+    }
+}

src/Massenger.Server/Controllers/ChatsController.cs

@@ -0,0 +1,479 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+using Massenger.Server.Infrastructure;
+using Massenger.Server.Infrastructure.Hubs;
+using Massenger.Server.Infrastructure.Push;
+using Massenger.Server.Infrastructure.Storage;
+using Massenger.Shared;
+using System.Net.Mime;
+
+namespace Massenger.Server.Controllers;
+
+[ApiController]
+[Authorize]
+[Route("api/[controller]")]
+public sealed class ChatsController(
+    MassengerDbContext dbContext,
+    PresenceTracker presenceTracker,
+    IHubContext<MessengerHub> hubContext,
+    AttachmentStorageService attachmentStorageService,
+    PushNotificationDispatcher pushNotificationDispatcher) : ControllerBase
+{
+    private const long MaxAttachmentSizeBytes = 25 * 1024 * 1024;
+
+    [HttpGet]
+    public async Task<ActionResult<IReadOnlyList<ChatSummaryDto>>> GetChats(CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+
+        var chats = await dbContext.ChatMembers
+            .Where(x => x.UserId == userId)
+            .Select(x => x.Chat)
+            .Include(x => x.Members)
+                .ThenInclude(x => x.User)
+            .Include(x => x.Messages)
+                .ThenInclude(x => x.Sender)
+            .Include(x => x.Messages)
+                .ThenInclude(x => x.Attachments)
+            .AsSplitQuery()
+            .ToListAsync(cancellationToken);
+
+        return Ok(chats
+            .OrderByDescending(x => x.LastActivityAt ?? x.CreatedAt)
+            .Select(x => x.ToSummaryDto(userId, presenceTracker))
+            .ToList());
+    }
+
+    [HttpGet("{chatId:guid}")]
+    public async Task<ActionResult<ChatDetailsDto>> GetChat(Guid chatId, CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var chat = await LoadChatWithMessages(chatId, userId, cancellationToken);
+
+        return chat is null
+            ? NotFound()
+            : Ok(chat.ToDetailsDto(userId, presenceTracker));
+    }
+
+    [HttpPost("direct")]
+    public async Task<ActionResult<ChatDetailsDto>> CreateDirectChat(CreateDirectChatRequest request, CancellationToken cancellationToken)
+    {
+        var currentUserId = User.GetRequiredUserId();
+        if (request.UserId == currentUserId)
+        {
+            return BadRequest("You cannot create a direct chat with yourself.");
+        }
+
+        var otherUserExists = await dbContext.Users.AnyAsync(x => x.Id == request.UserId, cancellationToken);
+        if (!otherUserExists)
+        {
+            return NotFound("User not found.");
+        }
+
+        var existingChat = await dbContext.Chats
+            .Include(x => x.Members)
+                .ThenInclude(x => x.User)
+            .Include(x => x.Messages)
+                .ThenInclude(x => x.Sender)
+            .Include(x => x.Messages)
+                .ThenInclude(x => x.Attachments)
+            .AsSplitQuery()
+            .SingleOrDefaultAsync(x =>
+                x.Type == ChatType.Direct &&
+                x.Members.Count == 2 &&
+                x.Members.Any(m => m.UserId == currentUserId) &&
+                x.Members.Any(m => m.UserId == request.UserId),
+                cancellationToken);
+
+        if (existingChat is not null)
+        {
+            return Ok(existingChat.ToDetailsDto(currentUserId, presenceTracker));
+        }
+
+        var chat = new Chat
+        {
+            Type = ChatType.Direct,
+            CreatedById = currentUserId,
+            LastActivityAt = DateTimeOffset.UtcNow,
+            Members =
+            [
+                new ChatMember { UserId = currentUserId, IsOwner = true },
+                new ChatMember { UserId = request.UserId, IsOwner = false }
+            ]
+        };
+
+        dbContext.Chats.Add(chat);
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var loaded = await LoadChatWithMessages(chat.Id, currentUserId, cancellationToken)
+            ?? throw new InvalidOperationException("Newly created chat could not be loaded.");
+
+        await NotifyChatCreatedAsync(loaded, cancellationToken);
+        return Ok(loaded.ToDetailsDto(currentUserId, presenceTracker));
+    }
+
+    [HttpPost("group")]
+    public async Task<ActionResult<ChatDetailsDto>> CreateGroupChat(CreateGroupChatRequest request, CancellationToken cancellationToken)
+    {
+        var currentUserId = User.GetRequiredUserId();
+        var memberIds = request.MemberIds
+            .Append(currentUserId)
+            .Distinct()
+            .ToList();
+
+        if (string.IsNullOrWhiteSpace(request.Title) || memberIds.Count < 3)
+        {
+            return BadRequest("A title and at least 2 invited members are required for a group chat.");
+        }
+
+        var users = await dbContext.Users
+            .Where(x => memberIds.Contains(x.Id))
+            .Select(x => x.Id)
+            .ToListAsync(cancellationToken);
+
+        if (users.Count != memberIds.Count)
+        {
+            return BadRequest("Some group members do not exist.");
+        }
+
+        var chat = new Chat
+        {
+            Type = ChatType.Group,
+            Title = request.Title.Trim(),
+            CreatedById = currentUserId,
+            LastActivityAt = DateTimeOffset.UtcNow,
+            Members = memberIds
+                .Select(x => new ChatMember { UserId = x, IsOwner = x == currentUserId })
+                .ToList()
+        };
+
+        dbContext.Chats.Add(chat);
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var loaded = await LoadChatWithMessages(chat.Id, currentUserId, cancellationToken)
+            ?? throw new InvalidOperationException("Newly created group chat could not be loaded.");
+
+        await NotifyChatCreatedAsync(loaded, cancellationToken);
+        return Ok(loaded.ToDetailsDto(currentUserId, presenceTracker));
+    }
+
+    [HttpPost("channel")]
+    public async Task<ActionResult<ChatDetailsDto>> CreateChannel(CreateChannelRequest request, CancellationToken cancellationToken)
+    {
+        var currentUserId = User.GetRequiredUserId();
+        var memberIds = request.MemberIds
+            .Append(currentUserId)
+            .Distinct()
+            .ToList();
+
+        if (string.IsNullOrWhiteSpace(request.Title))
+        {
+            return BadRequest("Channel title is required.");
+        }
+
+        var users = await dbContext.Users
+            .Where(x => memberIds.Contains(x.Id))
+            .Select(x => x.Id)
+            .ToListAsync(cancellationToken);
+
+        if (users.Count != memberIds.Count)
+        {
+            return BadRequest("Some channel members do not exist.");
+        }
+
+        var chat = new Chat
+        {
+            Type = ChatType.Channel,
+            Title = request.Title.Trim(),
+            CreatedById = currentUserId,
+            LastActivityAt = DateTimeOffset.UtcNow,
+            Members = memberIds
+                .Select(x => new ChatMember { UserId = x, IsOwner = x == currentUserId })
+                .ToList()
+        };
+
+        dbContext.Chats.Add(chat);
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var loaded = await LoadChatWithMessages(chat.Id, currentUserId, cancellationToken)
+            ?? throw new InvalidOperationException("Newly created channel could not be loaded.");
+
+        await NotifyChatCreatedAsync(loaded, cancellationToken);
+        return Ok(loaded.ToDetailsDto(currentUserId, presenceTracker));
+    }
+
+    [HttpPost("{chatId:guid}/messages")]
+    public async Task<ActionResult<MessageDto>> SendMessage(Guid chatId, SendMessageRequest request, CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var text = request.Text.Trim();
+        if (string.IsNullOrWhiteSpace(text))
+        {
+            return BadRequest("Message text is required.");
+        }
+
+        var chat = await dbContext.Chats
+            .Include(x => x.Members)
+            .FirstOrDefaultAsync(x => x.Id == chatId && x.Members.Any(m => m.UserId == userId), cancellationToken);
+
+        if (chat is null)
+        {
+            return NotFound();
+        }
+
+        if (!CanUserPublish(chat, userId))
+        {
+            return StatusCode(StatusCodes.Status403Forbidden, "Only channel owners can publish.");
+        }
+
+        var sender = await dbContext.Users.SingleAsync(x => x.Id == userId, cancellationToken);
+        var message = new Message
+        {
+            ChatId = chatId,
+            SenderId = userId,
+            Sender = sender,
+            Text = text,
+            SentAt = DateTimeOffset.UtcNow
+        };
+
+        chat.LastActivityAt = message.SentAt;
+        dbContext.Messages.Add(message);
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var dto = message.ToDto(presenceTracker);
+        await NotifyMessageCreatedAsync(chat, dto, cancellationToken);
+        await pushNotificationDispatcher.DispatchMessageAsync(chat, message, cancellationToken);
+
+        return Ok(dto);
+    }
+
+    [HttpPost("{chatId:guid}/attachments")]
+    [RequestFormLimits(MultipartBodyLengthLimit = MaxAttachmentSizeBytes)]
+    [RequestSizeLimit(MaxAttachmentSizeBytes)]
+    public async Task<ActionResult<MessageDto>> UploadAttachment(
+        Guid chatId,
+        [FromForm] UploadAttachmentRequest request,
+        CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        if (request.File is null)
+        {
+            return BadRequest("File is required.");
+        }
+
+        if (request.File.Length <= 0)
+        {
+            return BadRequest("File is empty.");
+        }
+
+        if (request.File.Length > MaxAttachmentSizeBytes)
+        {
+            return BadRequest($"File exceeds {MaxAttachmentSizeBytes} bytes.");
+        }
+
+        var chat = await dbContext.Chats
+            .Include(x => x.Members)
+            .FirstOrDefaultAsync(x => x.Id == chatId && x.Members.Any(m => m.UserId == userId), cancellationToken);
+
+        if (chat is null)
+        {
+            return NotFound();
+        }
+
+        if (!CanUserPublish(chat, userId))
+        {
+            return StatusCode(StatusCodes.Status403Forbidden, "Only channel owners can publish.");
+        }
+
+        var sender = await dbContext.Users.SingleAsync(x => x.Id == userId, cancellationToken);
+        var text = request.Text?.Trim() ?? string.Empty;
+        var message = new Message
+        {
+            ChatId = chatId,
+            SenderId = userId,
+            Sender = sender,
+            Text = text,
+            SentAt = DateTimeOffset.UtcNow
+        };
+
+        MessageAttachment? attachment = null;
+        try
+        {
+            attachment = await attachmentStorageService.SaveAsync(message.Id, request.File, cancellationToken);
+            message.Attachments.Add(attachment);
+            chat.LastActivityAt = message.SentAt;
+            dbContext.Messages.Add(message);
+            await dbContext.SaveChangesAsync(cancellationToken);
+        }
+        catch
+        {
+            if (attachment is not null)
+            {
+                attachmentStorageService.DeleteIfExists(attachment.StoragePath);
+            }
+
+            throw;
+        }
+
+        var dto = message.ToDto(presenceTracker);
+        await NotifyMessageCreatedAsync(chat, dto, cancellationToken);
+        await pushNotificationDispatcher.DispatchMessageAsync(chat, message, cancellationToken);
+
+        return Ok(dto);
+    }
+
+    [HttpPut("{chatId:guid}/messages/{messageId:guid}")]
+    public async Task<ActionResult<MessageDto>> UpdateMessage(
+        Guid chatId,
+        Guid messageId,
+        UpdateMessageRequest request,
+        CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var message = await LoadMessageForMemberAsync(chatId, messageId, userId, cancellationToken);
+        if (message is null)
+        {
+            return NotFound();
+        }
+
+        if (message.SenderId != userId)
+        {
+            return StatusCode(StatusCodes.Status403Forbidden, "Only the message author can edit it.");
+        }
+
+        if (message.DeletedAt is not null)
+        {
+            return BadRequest("Deleted messages cannot be edited.");
+        }
+
+        var text = request.Text.Trim();
+        if (string.IsNullOrWhiteSpace(text) && message.Attachments.Count == 0)
+        {
+            return BadRequest("Message text is required.");
+        }
+
+        message.Text = text;
+        message.EditedAt = DateTimeOffset.UtcNow;
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var dto = message.ToDto(presenceTracker);
+        await NotifyMessageUpdatedAsync(message.Chat, dto, cancellationToken);
+        return Ok(dto);
+    }
+
+    [HttpDelete("{chatId:guid}/messages/{messageId:guid}")]
+    public async Task<ActionResult<MessageDto>> DeleteMessage(Guid chatId, Guid messageId, CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var message = await LoadMessageForMemberAsync(chatId, messageId, userId, cancellationToken);
+        if (message is null)
+        {
+            return NotFound();
+        }
+
+        if (message.SenderId != userId)
+        {
+            return StatusCode(StatusCodes.Status403Forbidden, "Only the message author can delete it.");
+        }
+
+        if (message.DeletedAt is not null)
+        {
+            return Ok(message.ToDto(presenceTracker));
+        }
+
+        var attachments = message.Attachments.ToList();
+        foreach (var attachment in attachments)
+        {
+            attachmentStorageService.DeleteIfExists(attachment.StoragePath);
+        }
+
+        dbContext.MessageAttachments.RemoveRange(attachments);
+        message.Attachments.Clear();
+        message.Text = string.Empty;
+        message.EditedAt = null;
+        message.DeletedAt = DateTimeOffset.UtcNow;
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        var dto = message.ToDto(presenceTracker);
+        await NotifyMessageUpdatedAsync(message.Chat, dto, cancellationToken);
+        return Ok(dto);
+    }
+
+    [HttpGet("{chatId:guid}/attachments/{attachmentId:guid}/content")]
+    public async Task<IActionResult> DownloadAttachment(Guid chatId, Guid attachmentId, CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var attachment = await dbContext.MessageAttachments
+            .Include(x => x.Message)
+                .ThenInclude(x => x.Chat)
+                    .ThenInclude(x => x.Members)
+            .SingleOrDefaultAsync(
+                x => x.Id == attachmentId &&
+                     x.Message.ChatId == chatId &&
+                     x.Message.Chat.Members.Any(m => m.UserId == userId),
+                cancellationToken);
+
+        if (attachment is null || !System.IO.File.Exists(attachment.StoragePath))
+        {
+            return NotFound();
+        }
+
+        var stream = System.IO.File.OpenRead(attachment.StoragePath);
+        return File(stream, string.IsNullOrWhiteSpace(attachment.ContentType) ? MediaTypeNames.Application.Octet : attachment.ContentType, attachment.OriginalFileName);
+    }
+
+    private async Task<Chat?> LoadChatWithMessages(Guid chatId, Guid userId, CancellationToken cancellationToken)
+    {
+        return await dbContext.Chats
+            .Include(x => x.Members)
+                .ThenInclude(x => x.User)
+            .Include(x => x.Messages)
+                .ThenInclude(x => x.Sender)
+            .Include(x => x.Messages)
+                .ThenInclude(x => x.Attachments)
+            .AsSplitQuery()
+            .SingleOrDefaultAsync(x => x.Id == chatId && x.Members.Any(m => m.UserId == userId), cancellationToken);
+    }
+
+    private async Task<Message?> LoadMessageForMemberAsync(Guid chatId, Guid messageId, Guid userId, CancellationToken cancellationToken)
+    {
+        return await dbContext.Messages
+            .Include(x => x.Chat)
+                .ThenInclude(x => x.Members)
+            .Include(x => x.Sender)
+            .Include(x => x.Attachments)
+            .SingleOrDefaultAsync(
+                x => x.Id == messageId &&
+                     x.ChatId == chatId &&
+                     x.Chat.Members.Any(m => m.UserId == userId),
+                cancellationToken);
+    }
+
+    private static bool CanUserPublish(Chat chat, Guid userId) =>
+        chat.Type != ChatType.Channel || chat.Members.Any(x => x.UserId == userId && x.IsOwner);
+
+    private Task NotifyMessageCreatedAsync(Chat chat, MessageDto dto, CancellationToken cancellationToken) =>
+        hubContext.Clients.Users(chat.Members.Select(x => x.UserId.ToString()))
+            .SendAsync("MessageCreated", dto, cancellationToken);
+
+    private Task NotifyMessageUpdatedAsync(Chat chat, MessageDto dto, CancellationToken cancellationToken) =>
+        hubContext.Clients.Users(chat.Members.Select(x => x.UserId.ToString()))
+            .SendAsync("MessageUpdated", dto, cancellationToken);
+
+    private async Task NotifyChatCreatedAsync(Chat chat, CancellationToken cancellationToken)
+    {
+        foreach (var member in chat.Members)
+        {
+            var summary = chat.ToSummaryDto(member.UserId, presenceTracker);
+            await hubContext.Clients.User(member.UserId.ToString())
+                .SendAsync("ChatCreated", summary, cancellationToken);
+        }
+
+        await hubContext.Clients.Users(chat.Members.Select(x => x.UserId.ToString()))
+            .SendAsync("ChatsChanged", cancellationToken);
+    }
+}

src/Massenger.Server/Controllers/PushController.cs

@@ -0,0 +1,107 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+using Massenger.Server.Infrastructure;
+using Massenger.Shared;
+
+namespace Massenger.Server.Controllers;
+
+[ApiController]
+[Authorize]
+[Route("api/[controller]")]
+public sealed class PushController(MassengerDbContext dbContext) : ControllerBase
+{
+    [HttpGet("devices")]
+    public async Task<ActionResult<IReadOnlyList<PushDeviceDto>>> GetDevices(CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var devices = await dbContext.PushDevices
+            .Where(x => x.UserId == userId)
+            .ToListAsync(cancellationToken);
+
+        return Ok(devices
+            .OrderByDescending(x => x.UpdatedAt)
+            .Select(x => x.ToDto())
+            .ToList());
+    }
+
+    [HttpPost("devices")]
+    public async Task<ActionResult<PushDeviceDto>> RegisterDevice(
+        RegisterPushDeviceRequest request,
+        CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        if (request.Platform == PushPlatform.Unknown ||
+            string.IsNullOrWhiteSpace(request.InstallationId) ||
+            string.IsNullOrWhiteSpace(request.DeviceToken))
+        {
+            return ValidationProblem("Platform, installationId and deviceToken are required.");
+        }
+
+        var installationId = request.InstallationId.Trim();
+        var device = await dbContext.PushDevices
+            .SingleOrDefaultAsync(x => x.InstallationId == installationId, cancellationToken);
+
+        if (device is null)
+        {
+            device = new PushDevice
+            {
+                UserId = userId,
+                Platform = request.Platform,
+                InstallationId = installationId,
+                DeviceToken = request.DeviceToken.Trim(),
+                DeviceName = NormalizeDeviceName(request.DeviceName),
+                NotificationsEnabled = request.NotificationsEnabled,
+                UpdatedAt = DateTimeOffset.UtcNow
+            };
+
+            dbContext.PushDevices.Add(device);
+        }
+        else
+        {
+            device.UserId = userId;
+            device.Platform = request.Platform;
+            device.DeviceToken = request.DeviceToken.Trim();
+            device.DeviceName = NormalizeDeviceName(request.DeviceName);
+            device.NotificationsEnabled = request.NotificationsEnabled;
+            device.UpdatedAt = DateTimeOffset.UtcNow;
+        }
+
+        await dbContext.SaveChangesAsync(cancellationToken);
+        return Ok(device.ToDto());
+    }
+
+    [HttpDelete("devices/{installationId}")]
+    public async Task<IActionResult> UnregisterDevice(string installationId, CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var normalizedInstallationId = installationId.Trim();
+        if (string.IsNullOrWhiteSpace(normalizedInstallationId))
+        {
+            return NotFound();
+        }
+
+        var device = await dbContext.PushDevices
+            .SingleOrDefaultAsync(
+                x => x.InstallationId == normalizedInstallationId &&
+                     x.UserId == userId,
+                cancellationToken);
+
+        if (device is null)
+        {
+            return NotFound();
+        }
+
+        dbContext.PushDevices.Remove(device);
+        await dbContext.SaveChangesAsync(cancellationToken);
+        return NoContent();
+    }
+
+    private static string? NormalizeDeviceName(string? deviceName)
+    {
+        var normalized = deviceName?.Trim();
+        return string.IsNullOrWhiteSpace(normalized) ? null : normalized;
+    }
+}

src/Massenger.Server/Controllers/UploadAttachmentRequest.cs

@@ -0,0 +1,8 @@
+namespace Massenger.Server.Controllers;
+
+public sealed class UploadAttachmentRequest
+{
+    public string? Text { get; set; }
+
+    public IFormFile? File { get; set; }
+}

src/Massenger.Server/Controllers/UsersController.cs

@@ -0,0 +1,47 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+using Massenger.Server.Infrastructure;
+using Massenger.Shared;
+
+namespace Massenger.Server.Controllers;
+
+[ApiController]
+[Authorize]
+[Route("api/[controller]")]
+public sealed class UsersController(
+    MassengerDbContext dbContext,
+    PresenceTracker presenceTracker) : ControllerBase
+{
+    [HttpGet("me")]
+    public async Task<ActionResult<UserSummaryDto>> GetMe(CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var user = await dbContext.Users.SingleAsync(x => x.Id == userId, cancellationToken);
+        return Ok(user.ToDto(presenceTracker));
+    }
+
+    [HttpGet("search")]
+    public async Task<ActionResult<IReadOnlyList<UserSummaryDto>>> Search([FromQuery] string? q, CancellationToken cancellationToken)
+    {
+        var userId = User.GetRequiredUserId();
+        var query = q?.Trim();
+
+        var usersQuery = dbContext.Users.Where(x => x.Id != userId);
+        if (!string.IsNullOrWhiteSpace(query))
+        {
+            var normalized = query.ToUpperInvariant();
+            usersQuery = usersQuery.Where(x =>
+                x.NormalizedUsername.Contains(normalized) ||
+                EF.Functions.Like(x.DisplayName, $"%{query}%"));
+        }
+
+        var users = await usersQuery
+            .OrderBy(x => x.DisplayName)
+            .Take(25)
+            .ToListAsync(cancellationToken);
+
+        return Ok(users.Select(x => x.ToDto(presenceTracker)).ToList());
+    }
+}

src/Massenger.Server/Infrastructure/Auth/JwtOptions.cs

@@ -0,0 +1,16 @@
+namespace Massenger.Server.Infrastructure.Auth;
+
+public sealed class JwtOptions
+{
+    public const string SectionName = "Jwt";
+
+    public string Issuer { get; init; } = "Massenger.Server";
+
+    public string Audience { get; init; } = "Massenger.Client";
+
+    public string SigningKey { get; init; } = "Massenger-Replace-This-Development-Key-With-A-Long-Random-Secret-123456789";
+
+    public int AccessTokenLifetimeMinutes { get; init; } = 15;
+
+    public int RefreshTokenLifetimeDays { get; init; } = 30;
+}

src/Massenger.Server/Infrastructure/Auth/TokenService.cs

@@ -0,0 +1,120 @@
+using System.IdentityModel.Tokens.Jwt;
+using System.Security.Claims;
+using System.Security.Cryptography;
+using System.Text;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
+using Microsoft.IdentityModel.Tokens;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+using Massenger.Shared;
+
+namespace Massenger.Server.Infrastructure.Auth;
+
+public sealed class TokenService(
+    MassengerDbContext dbContext,
+    IOptions<JwtOptions> jwtOptions)
+{
+    private readonly JwtOptions _jwtOptions = jwtOptions.Value;
+
+    public async Task<AuthSessionDto> CreateSessionAsync(User user, CancellationToken cancellationToken = default)
+    {
+        var now = DateTimeOffset.UtcNow;
+        var session = new UserSession
+        {
+            UserId = user.Id,
+            LastSeenAt = now
+        };
+
+        var refreshToken = CreateOpaqueToken();
+        session.TokenHash = HashToken(refreshToken);
+        dbContext.UserSessions.Add(session);
+
+        await dbContext.SaveChangesAsync(cancellationToken);
+        return CreateAuthSession(user, session.Id, refreshToken, now);
+    }
+
+    public async Task<AuthSessionDto?> RefreshSessionAsync(string rawRefreshToken, CancellationToken cancellationToken = default)
+    {
+        var hash = HashToken(rawRefreshToken);
+        var session = await dbContext.UserSessions.SingleOrDefaultAsync(x => x.TokenHash == hash, cancellationToken);
+        if (session is null)
+        {
+            return null;
+        }
+
+        if (session.CreatedAt.AddDays(_jwtOptions.RefreshTokenLifetimeDays) <= DateTimeOffset.UtcNow)
+        {
+            dbContext.UserSessions.Remove(session);
+            await dbContext.SaveChangesAsync(cancellationToken);
+            return null;
+        }
+
+        var user = await dbContext.Users.SingleAsync(x => x.Id == session.UserId, cancellationToken);
+        var now = DateTimeOffset.UtcNow;
+        var refreshToken = CreateOpaqueToken();
+        session.TokenHash = HashToken(refreshToken);
+        session.CreatedAt = now;
+        session.LastSeenAt = now;
+        await dbContext.SaveChangesAsync(cancellationToken);
+
+        return CreateAuthSession(user, session.Id, refreshToken, now);
+    }
+
+    public async Task<bool> RevokeSessionAsync(Guid sessionId, CancellationToken cancellationToken = default)
+    {
+        var session = await dbContext.UserSessions.SingleOrDefaultAsync(x => x.Id == sessionId, cancellationToken);
+        if (session is null)
+        {
+            return false;
+        }
+
+        dbContext.UserSessions.Remove(session);
+        await dbContext.SaveChangesAsync(cancellationToken);
+        return true;
+    }
+
+    public static string HashToken(string token)
+    {
+        var hashBytes = SHA256.HashData(Encoding.UTF8.GetBytes(token));
+        return Convert.ToHexString(hashBytes);
+    }
+
+    private AuthSessionDto CreateAuthSession(User user, Guid sessionId, string refreshToken, DateTimeOffset now)
+    {
+        var accessTokenExpiresAt = now.AddMinutes(_jwtOptions.AccessTokenLifetimeMinutes);
+        var credentials = new SigningCredentials(
+            new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_jwtOptions.SigningKey)),
+            SecurityAlgorithms.HmacSha256);
+
+        var claims = new List<Claim>
+        {
+            new(ClaimTypes.NameIdentifier, user.Id.ToString()),
+            new(ClaimTypes.Name, user.DisplayName),
+            new("username", user.Username),
+            new("sid", sessionId.ToString()),
+            new(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString("N"))
+        };
+
+        var jwt = new JwtSecurityToken(
+            issuer: _jwtOptions.Issuer,
+            audience: _jwtOptions.Audience,
+            claims: claims,
+            notBefore: now.UtcDateTime,
+            expires: accessTokenExpiresAt.UtcDateTime,
+            signingCredentials: credentials);
+
+        var accessToken = new JwtSecurityTokenHandler().WriteToken(jwt);
+
+        return new AuthSessionDto(accessToken, refreshToken, accessTokenExpiresAt, new(user.Id, user.Username, user.DisplayName, false));
+    }
+
+    private static string CreateOpaqueToken()
+    {
+        var tokenBytes = RandomNumberGenerator.GetBytes(32);
+        return Convert.ToBase64String(tokenBytes)
+            .TrimEnd('=')
+            .Replace('+', '-')
+            .Replace('/', '_');
+    }
+}

src/Massenger.Server/Infrastructure/ClaimsPrincipalExtensions.cs

@@ -0,0 +1,22 @@
+using System.Security.Claims;
+
+namespace Massenger.Server.Infrastructure;
+
+public static class ClaimsPrincipalExtensions
+{
+    public static Guid GetRequiredUserId(this ClaimsPrincipal principal)
+    {
+        var value = principal.FindFirstValue(ClaimTypes.NameIdentifier);
+        return Guid.TryParse(value, out var userId)
+            ? userId
+            : throw new InvalidOperationException("Authenticated user id claim is missing.");
+    }
+
+    public static Guid GetRequiredSessionId(this ClaimsPrincipal principal)
+    {
+        var value = principal.FindFirstValue("sid");
+        return Guid.TryParse(value, out var sessionId)
+            ? sessionId
+            : throw new InvalidOperationException("Authenticated session id claim is missing.");
+    }
+}

src/Massenger.Server/Infrastructure/DatabaseSeeder.cs

@@ -0,0 +1,116 @@
+using Microsoft.AspNetCore.Identity;
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+using Massenger.Shared;
+
+namespace Massenger.Server.Infrastructure;
+
+public sealed class DatabaseSeeder(MassengerDbContext dbContext)
+{
+    private readonly PasswordHasher<User> _passwordHasher = new();
+
+    public async Task SeedAsync()
+    {
+        if (await dbContext.Users.AnyAsync())
+        {
+            return;
+        }
+
+        var alice = CreateUser("alice", "Alice Carter", "demo123");
+        var bob = CreateUser("bob", "Bob Miller", "demo123");
+        var carol = CreateUser("carol", "Carol Stone", "demo123");
+
+        var directChat = new Chat
+        {
+            Type = ChatType.Direct,
+            CreatedBy = alice,
+            CreatedAt = DateTimeOffset.UtcNow.AddMinutes(-30),
+            LastActivityAt = DateTimeOffset.UtcNow.AddMinutes(-5),
+            Members =
+            [
+                new ChatMember { User = alice, IsOwner = true, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-30) },
+                new ChatMember { User = bob, IsOwner = false, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-30) }
+            ]
+        };
+
+        var groupChat = new Chat
+        {
+            Type = ChatType.Group,
+            Title = "Massenger Crew",
+            CreatedBy = alice,
+            CreatedAt = DateTimeOffset.UtcNow.AddMinutes(-20),
+            LastActivityAt = DateTimeOffset.UtcNow.AddMinutes(-2),
+            Members =
+            [
+                new ChatMember { User = alice, IsOwner = true, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-20) },
+                new ChatMember { User = bob, IsOwner = false, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-20) },
+                new ChatMember { User = carol, IsOwner = false, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-20) }
+            ]
+        };
+
+        directChat.Messages.Add(new Message
+        {
+            Chat = directChat,
+            Sender = alice,
+            Text = "Welcome to Massenger. This is a seeded private dialog.",
+            SentAt = DateTimeOffset.UtcNow.AddMinutes(-10)
+        });
+
+        directChat.Messages.Add(new Message
+        {
+            Chat = directChat,
+            Sender = bob,
+            Text = "Messages are stored in SQLite and delivered through SignalR.",
+            SentAt = DateTimeOffset.UtcNow.AddMinutes(-5)
+        });
+
+        groupChat.Messages.Add(new Message
+        {
+            Chat = groupChat,
+            Sender = carol,
+            Text = "Use this group to validate shared conversations.",
+            SentAt = DateTimeOffset.UtcNow.AddMinutes(-2)
+        });
+
+        var channel = new Chat
+        {
+            Type = ChatType.Channel,
+            Title = "Massenger Updates",
+            CreatedBy = alice,
+            CreatedAt = DateTimeOffset.UtcNow.AddMinutes(-15),
+            LastActivityAt = DateTimeOffset.UtcNow.AddMinutes(-1),
+            Members =
+            [
+                new ChatMember { User = alice, IsOwner = true, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-15) },
+                new ChatMember { User = bob, IsOwner = false, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-15) },
+                new ChatMember { User = carol, IsOwner = false, JoinedAt = DateTimeOffset.UtcNow.AddMinutes(-15) }
+            ]
+        };
+
+        channel.Messages.Add(new Message
+        {
+            Chat = channel,
+            Sender = alice,
+            Text = "This channel is broadcast-only. Owners can post, subscribers can read.",
+            SentAt = DateTimeOffset.UtcNow.AddMinutes(-1)
+        });
+
+        dbContext.Users.AddRange(alice, bob, carol);
+        dbContext.Chats.AddRange(directChat, groupChat, channel);
+        await dbContext.SaveChangesAsync();
+    }
+
+    private User CreateUser(string username, string displayName, string password)
+    {
+        var user = new User
+        {
+            Username = username,
+            NormalizedUsername = username.ToUpperInvariant(),
+            DisplayName = displayName
+        };
+
+        user.PasswordHash = _passwordHasher.HashPassword(user, password);
+        return user;
+    }
+}

src/Massenger.Server/Infrastructure/DtoMapper.cs

@@ -0,0 +1,203 @@
+using Massenger.Server.Data.Entities;
+using Massenger.Shared;
+
+namespace Massenger.Server.Infrastructure;
+
+public static class DtoMapper
+{
+    private static readonly HashSet<string> AudioExtensions =
+    [
+        ".aac",
+        ".flac",
+        ".m4a",
+        ".mp3",
+        ".oga",
+        ".ogg",
+        ".opus",
+        ".wav",
+        ".webm"
+    ];
+
+    public static UserSummaryDto ToDto(this User user, PresenceTracker presenceTracker) =>
+        new(
+            user.Id,
+            user.Username,
+            user.DisplayName,
+            presenceTracker.IsOnline(user.Id));
+
+    public static PushDeviceDto ToDto(this PushDevice device) =>
+        new(
+            device.Id,
+            device.Platform,
+            device.InstallationId,
+            device.DeviceName,
+            device.NotificationsEnabled,
+            device.UpdatedAt);
+
+    public static MessageDto ToDto(this Message message, PresenceTracker presenceTracker) =>
+        new(
+            message.Id,
+            message.ChatId,
+            message.Sender.ToDto(presenceTracker),
+            message.Text,
+            message.Attachments
+                .OrderBy(x => x.OriginalFileName)
+                .Select(x => x.ToDto(message.ChatId))
+                .ToList(),
+            message.SentAt,
+            message.EditedAt,
+            message.DeletedAt);
+
+    public static AttachmentDto ToDto(this MessageAttachment attachment, Guid chatId) =>
+        new(
+            attachment.Id,
+            attachment.OriginalFileName,
+            attachment.ContentType,
+            attachment.FileSizeBytes,
+            $"/api/chats/{chatId}/attachments/{attachment.Id}/content",
+            ResolveAttachmentKind(attachment));
+
+    public static ChatSummaryDto ToSummaryDto(this Chat chat, Guid currentUserId, PresenceTracker presenceTracker)
+    {
+        var orderedMembers = chat.Members
+            .Select(x => x.User)
+            .OrderBy(x => x.DisplayName)
+            .ToList();
+
+        var participants = orderedMembers
+            .Select(user => user.ToDto(presenceTracker))
+            .ToList();
+
+        var counterpart = chat.Type == ChatType.Direct
+            ? orderedMembers.FirstOrDefault(x => x.Id != currentUserId)
+            : null;
+        var currentMembership = chat.Members.FirstOrDefault(x => x.UserId == currentUserId);
+        var canSendMessages = chat.Type != ChatType.Channel || currentMembership?.IsOwner == true;
+
+        var title = chat.Type == ChatType.Direct
+            ? counterpart?.DisplayName ?? "Dialog"
+            : string.IsNullOrWhiteSpace(chat.Title) ? "New Group" : chat.Title;
+
+        var secondary = chat.Type switch
+        {
+            ChatType.Direct => counterpart is null ? null : $"@{counterpart.Username}",
+            ChatType.Channel => $"{chat.Members.Count(x => !x.IsOwner)} subscribers{(canSendMessages ? " | owner can post" : " | read-only")}",
+            _ => $"{participants.Count} members"
+        };
+
+        var lastMessage = chat.Messages.OrderByDescending(x => x.SentAt).FirstOrDefault();
+        var lastPreview = lastMessage is null ? null : BuildMessagePreview(lastMessage);
+
+        return new ChatSummaryDto(
+            chat.Id,
+            title,
+            chat.Type,
+            secondary,
+            chat.LastActivityAt ?? chat.CreatedAt,
+            lastPreview,
+            participants,
+            canSendMessages);
+    }
+
+    public static ChatDetailsDto ToDetailsDto(this Chat chat, Guid currentUserId, PresenceTracker presenceTracker)
+    {
+        var participants = chat.Members
+            .Select(x => x.User)
+            .OrderBy(x => x.DisplayName)
+            .Select(x => x.ToDto(presenceTracker))
+            .ToList();
+
+        var counterpart = chat.Type == ChatType.Direct
+            ? chat.Members.Select(x => x.User).FirstOrDefault(x => x.Id != currentUserId)
+            : null;
+        var currentMembership = chat.Members.FirstOrDefault(x => x.UserId == currentUserId);
+        var canSendMessages = chat.Type != ChatType.Channel || currentMembership?.IsOwner == true;
+
+        var title = chat.Type == ChatType.Direct
+            ? counterpart?.DisplayName ?? "Dialog"
+            : string.IsNullOrWhiteSpace(chat.Title) ? "New Group" : chat.Title;
+
+        var messages = chat.Messages
+            .OrderBy(x => x.SentAt)
+            .Select(x => x.ToDto(presenceTracker))
+            .ToList();
+
+        return new ChatDetailsDto(chat.Id, title, chat.Type, participants, canSendMessages, messages);
+    }
+
+    public static string BuildPushTitle(this Chat chat, Message message) =>
+        chat.Type switch
+        {
+            ChatType.Direct => message.Sender.DisplayName,
+            _ => string.IsNullOrWhiteSpace(chat.Title) ? message.Sender.DisplayName : chat.Title!
+        };
+
+    public static string BuildPushBody(this Message message)
+    {
+        if (message.DeletedAt is not null)
+        {
+            return "Message removed";
+        }
+
+        if (!string.IsNullOrWhiteSpace(message.Text))
+        {
+            return message.Attachments.Count == 0
+                ? message.Text
+                : $"{message.Text} ({BuildAttachmentPreview(message.Attachments)})";
+        }
+
+        return BuildAttachmentPreview(message.Attachments);
+    }
+
+    private static string BuildMessagePreview(Message lastMessage)
+    {
+        if (lastMessage.DeletedAt is not null)
+        {
+            return $"{lastMessage.Sender.DisplayName}: message removed";
+        }
+
+        if (string.IsNullOrWhiteSpace(lastMessage.Text))
+        {
+            return $"{lastMessage.Sender.DisplayName}: {BuildAttachmentPreview(lastMessage.Attachments)}";
+        }
+
+        return lastMessage.Attachments.Count == 0
+            ? $"{lastMessage.Sender.DisplayName}: {lastMessage.Text}"
+            : $"{lastMessage.Sender.DisplayName}: {lastMessage.Text} ({BuildAttachmentPreview(lastMessage.Attachments)})";
+    }
+
+    private static string BuildAttachmentPreview(IReadOnlyCollection<MessageAttachment> attachments)
+    {
+        if (attachments.Count == 0)
+        {
+            return string.Empty;
+        }
+
+        if (attachments.Count == 1)
+        {
+            var attachment = attachments.First();
+            return ResolveAttachmentKind(attachment) == AttachmentKind.VoiceNote
+                ? "voice note"
+                : $"file: {attachment.OriginalFileName}";
+        }
+
+        return $"{attachments.Count} files";
+    }
+
+    private static AttachmentKind ResolveAttachmentKind(MessageAttachment attachment) =>
+        IsAudioAttachment(attachment.ContentType, attachment.OriginalFileName)
+            ? AttachmentKind.VoiceNote
+            : AttachmentKind.File;
+
+    private static bool IsAudioAttachment(string? contentType, string? fileName)
+    {
+        if (!string.IsNullOrWhiteSpace(contentType) &&
+            contentType.StartsWith("audio/", StringComparison.OrdinalIgnoreCase))
+        {
+            return true;
+        }
+
+        var extension = Path.GetExtension(fileName ?? string.Empty);
+        return AudioExtensions.Contains(extension);
+    }
+}

src/Massenger.Server/Infrastructure/Hubs/MessengerHub.cs

@@ -0,0 +1,20 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.SignalR;
+
+namespace Massenger.Server.Infrastructure.Hubs;
+
+[Authorize]
+public sealed class MessengerHub(PresenceTracker presenceTracker) : Hub
+{
+    public override Task OnConnectedAsync()
+    {
+        presenceTracker.MarkOnline(Context.User!.GetRequiredUserId());
+        return base.OnConnectedAsync();
+    }
+
+    public override Task OnDisconnectedAsync(Exception? exception)
+    {
+        presenceTracker.MarkOffline(Context.User!.GetRequiredUserId());
+        return base.OnDisconnectedAsync(exception);
+    }
+}

src/Massenger.Server/Infrastructure/PresenceTracker.cs

@@ -0,0 +1,41 @@
+using System.Collections.Concurrent;
+
+namespace Massenger.Server.Infrastructure;
+
+public sealed class PresenceTracker
+{
+    private readonly ConcurrentDictionary<Guid, int> _connections = new();
+
+    public void MarkOnline(Guid userId)
+    {
+        _connections.AddOrUpdate(userId, 1, (_, current) => current + 1);
+    }
+
+    public void MarkOffline(Guid userId)
+    {
+        while (true)
+        {
+            if (!_connections.TryGetValue(userId, out var current))
+            {
+                return;
+            }
+
+            if (current <= 1)
+            {
+                if (_connections.TryRemove(userId, out _))
+                {
+                    return;
+                }
+
+                continue;
+            }
+
+            if (_connections.TryUpdate(userId, current - 1, current))
+            {
+                return;
+            }
+        }
+    }
+
+    public bool IsOnline(Guid userId) => _connections.ContainsKey(userId);
+}

src/Massenger.Server/Infrastructure/Push/FirebasePushNotificationSender.cs

@@ -0,0 +1,275 @@
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Microsoft.Extensions.Options;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+using Massenger.Shared;
+
+namespace Massenger.Server.Infrastructure.Push;
+
+public sealed class FirebasePushNotificationSender(
+    HttpClient httpClient,
+    IOptions<PushOptions> options,
+    IHostEnvironment hostEnvironment,
+    MassengerDbContext dbContext,
+    ILogger<FirebasePushNotificationSender> logger) : IPushNotificationSender
+{
+    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);
+    private readonly PushOptions _options = options.Value;
+    private readonly SemaphoreSlim _tokenLock = new(1, 1);
+
+    private OAuthTokenCache? _cachedToken;
+    private ServiceAccountCredentials? _cachedCredentials;
+
+    public async Task SendMessageAsync(
+        Chat chat,
+        Message message,
+        IReadOnlyCollection<PushDevice> devices,
+        CancellationToken cancellationToken = default)
+    {
+        var androidDevices = devices
+            .Where(x => x.Platform == PushPlatform.Android && !string.IsNullOrWhiteSpace(x.DeviceToken))
+            .ToList();
+
+        if (androidDevices.Count == 0)
+        {
+            return;
+        }
+
+        var credentials = LoadCredentials();
+        if (credentials is null)
+        {
+            logger.LogDebug("Firebase push is not configured. Skipping {DeviceCount} Android device(s).", androidDevices.Count);
+            return;
+        }
+
+        var projectId = string.IsNullOrWhiteSpace(_options.FirebaseProjectId)
+            ? credentials.ProjectId
+            : _options.FirebaseProjectId.Trim();
+
+        if (string.IsNullOrWhiteSpace(projectId))
+        {
+            logger.LogWarning("Push:FirebaseProjectId is empty and the service account JSON does not contain project_id.");
+            return;
+        }
+
+        var accessToken = await GetAccessTokenAsync(credentials, cancellationToken);
+        var title = chat.BuildPushTitle(message);
+        var body = message.BuildPushBody();
+
+        foreach (var device in androidDevices)
+        {
+            await SendToAndroidAsync(projectId, accessToken, device, title, body, message, cancellationToken);
+        }
+    }
+
+    private ServiceAccountCredentials? LoadCredentials()
+    {
+        if (_cachedCredentials is not null)
+        {
+            return _cachedCredentials;
+        }
+
+        var json = _options.ServiceAccountJson;
+        if (string.IsNullOrWhiteSpace(json) && !string.IsNullOrWhiteSpace(_options.ServiceAccountJsonPath))
+        {
+            var path = _options.ServiceAccountJsonPath;
+            if (!Path.IsPathRooted(path))
+            {
+                path = Path.Combine(hostEnvironment.ContentRootPath, path);
+            }
+
+            if (!File.Exists(path))
+            {
+                logger.LogWarning("Push service account file was not found: {Path}", path);
+                return null;
+            }
+
+            json = File.ReadAllText(path);
+        }
+
+        if (string.IsNullOrWhiteSpace(json))
+        {
+            return null;
+        }
+
+        try
+        {
+            var credentials = JsonSerializer.Deserialize<ServiceAccountCredentials>(json, JsonOptions);
+            if (credentials is null ||
+                string.IsNullOrWhiteSpace(credentials.ClientEmail) ||
+                string.IsNullOrWhiteSpace(credentials.PrivateKey))
+            {
+                logger.LogWarning("Push service account JSON is missing required fields.");
+                return null;
+            }
+
+            _cachedCredentials = credentials;
+            return credentials;
+        }
+        catch (JsonException ex)
+        {
+            logger.LogWarning(ex, "Push service account JSON could not be parsed.");
+            return null;
+        }
+    }
+
+    private async Task<string> GetAccessTokenAsync(ServiceAccountCredentials credentials, CancellationToken cancellationToken)
+    {
+        var now = DateTimeOffset.UtcNow;
+        if (_cachedToken is not null && _cachedToken.ExpiresAt > now.AddMinutes(5))
+        {
+            return _cachedToken.AccessToken;
+        }
+
+        await _tokenLock.WaitAsync(cancellationToken);
+        try
+        {
+            now = DateTimeOffset.UtcNow;
+            if (_cachedToken is not null && _cachedToken.ExpiresAt > now.AddMinutes(5))
+            {
+                return _cachedToken.AccessToken;
+            }
+
+            var assertion = CreateJwtAssertion(credentials, now);
+            using var request = new HttpRequestMessage(HttpMethod.Post, credentials.TokenUri ?? "https://oauth2.googleapis.com/token")
+            {
+                Content = new FormUrlEncodedContent(
+                [
+                    new KeyValuePair<string, string>("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer"),
+                    new KeyValuePair<string, string>("assertion", assertion)
+                ])
+            };
+
+            using var response = await httpClient.SendAsync(request, cancellationToken);
+            var payload = await response.Content.ReadAsStringAsync(cancellationToken);
+            if (!response.IsSuccessStatusCode)
+            {
+                throw new InvalidOperationException(
+                    string.IsNullOrWhiteSpace(payload)
+                        ? $"Failed to acquire Firebase access token: {(int)response.StatusCode}."
+                        : $"Failed to acquire Firebase access token: {payload}");
+            }
+
+            var tokenResponse = JsonSerializer.Deserialize<OAuthTokenResponse>(payload, JsonOptions)
+                ?? throw new InvalidOperationException("Firebase access token response was empty.");
+
+            _cachedToken = new OAuthTokenCache(
+                tokenResponse.AccessToken,
+                now.AddSeconds(tokenResponse.ExpiresIn));
+
+            return _cachedToken.AccessToken;
+        }
+        finally
+        {
+            _tokenLock.Release();
+        }
+    }
+
+    private async Task SendToAndroidAsync(
+        string projectId,
+        string accessToken,
+        PushDevice device,
+        string title,
+        string body,
+        Message message,
+        CancellationToken cancellationToken)
+    {
+        var payload = new
+        {
+            message = new
+            {
+                token = device.DeviceToken,
+                data = new Dictionary<string, string>
+                {
+                    [PushDataKeys.Kind] = PushDataKinds.ChatMessage,
+                    [PushDataKeys.ChatId] = message.ChatId.ToString(),
+                    [PushDataKeys.MessageId] = message.Id.ToString(),
+                    [PushDataKeys.Title] = title,
+                    [PushDataKeys.Body] = body,
+                    [PushDataKeys.SenderId] = message.SenderId.ToString(),
+                    [PushDataKeys.SenderName] = message.Sender.DisplayName
+                },
+                android = new
+                {
+                    priority = "high",
+                    ttl = "30s"
+                }
+            }
+        };
+
+        using var request = new HttpRequestMessage(
+            HttpMethod.Post,
+            $"https://fcm.googleapis.com/v1/projects/{projectId}/messages:send");
+        request.Headers.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", accessToken);
+        request.Content = new StringContent(JsonSerializer.Serialize(payload, JsonOptions), Encoding.UTF8, "application/json");
+
+        using var response = await httpClient.SendAsync(request, cancellationToken);
+        if (response.IsSuccessStatusCode)
+        {
+            return;
+        }
+
+        var responseBody = await response.Content.ReadAsStringAsync(cancellationToken);
+        logger.LogWarning(
+            "Push send failed for installation {InstallationId} with status {StatusCode}. Response: {ResponseBody}",
+            device.InstallationId,
+            (int)response.StatusCode,
+            responseBody);
+
+        if (!ShouldDeleteDevice(responseBody))
+        {
+            return;
+        }
+
+        dbContext.PushDevices.Remove(device);
+        await dbContext.SaveChangesAsync(cancellationToken);
+    }
+
+    private static bool ShouldDeleteDevice(string? responseBody) =>
+        !string.IsNullOrWhiteSpace(responseBody) &&
+        (responseBody.Contains("UNREGISTERED", StringComparison.OrdinalIgnoreCase) ||
+         responseBody.Contains("registration-token-not-registered", StringComparison.OrdinalIgnoreCase));
+
+    private static string CreateJwtAssertion(ServiceAccountCredentials credentials, DateTimeOffset now)
+    {
+        var header = Base64UrlEncode("""{"alg":"RS256","typ":"JWT"}""");
+        var payload = Base64UrlEncode(JsonSerializer.Serialize(new Dictionary<string, object>
+        {
+            ["iss"] = credentials.ClientEmail,
+            ["scope"] = "https://www.googleapis.com/auth/firebase.messaging",
+            ["aud"] = credentials.TokenUri ?? "https://oauth2.googleapis.com/token",
+            ["iat"] = now.ToUnixTimeSeconds(),
+            ["exp"] = now.AddHours(1).ToUnixTimeSeconds()
+        }));
+
+        var unsignedToken = $"{header}.{payload}";
+        using var rsa = RSA.Create();
+        rsa.ImportFromPem(credentials.PrivateKey);
+        var signatureBytes = rsa.SignData(Encoding.UTF8.GetBytes(unsignedToken), HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
+        return $"{unsignedToken}.{Base64UrlEncode(signatureBytes)}";
+    }
+
+    private static string Base64UrlEncode(string value) =>
+        Base64UrlEncode(Encoding.UTF8.GetBytes(value));
+
+    private static string Base64UrlEncode(byte[] value) =>
+        Convert.ToBase64String(value)
+            .TrimEnd('=')
+            .Replace('+', '-')
+            .Replace('/', '_');
+
+    private sealed record OAuthTokenCache(string AccessToken, DateTimeOffset ExpiresAt);
+
+    private sealed record OAuthTokenResponse(
+        [property: JsonPropertyName("access_token")] string AccessToken,
+        [property: JsonPropertyName("expires_in")] int ExpiresIn);
+
+    private sealed record ServiceAccountCredentials(
+        [property: JsonPropertyName("project_id")] string ProjectId,
+        [property: JsonPropertyName("client_email")] string ClientEmail,
+        [property: JsonPropertyName("private_key")] string PrivateKey,
+        [property: JsonPropertyName("token_uri")] string? TokenUri);
+}

src/Massenger.Server/Infrastructure/Push/IPushNotificationSender.cs

@@ -0,0 +1,12 @@
+using Massenger.Server.Data.Entities;
+
+namespace Massenger.Server.Infrastructure.Push;
+
+public interface IPushNotificationSender
+{
+    Task SendMessageAsync(
+        Chat chat,
+        Message message,
+        IReadOnlyCollection<PushDevice> devices,
+        CancellationToken cancellationToken = default);
+}

src/Massenger.Server/Infrastructure/Push/PushNotificationDispatcher.cs

@@ -0,0 +1,45 @@
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+using Massenger.Server.Data.Entities;
+
+namespace Massenger.Server.Infrastructure.Push;
+
+public sealed class PushNotificationDispatcher(
+    MassengerDbContext dbContext,
+    PresenceTracker presenceTracker,
+    IPushNotificationSender pushNotificationSender,
+    ILogger<PushNotificationDispatcher> logger)
+{
+    public async Task DispatchMessageAsync(Chat chat, Message message, CancellationToken cancellationToken = default)
+    {
+        var offlineRecipientIds = chat.Members
+            .Select(x => x.UserId)
+            .Where(x => x != message.SenderId)
+            .Where(x => !presenceTracker.IsOnline(x))
+            .Distinct()
+            .ToList();
+
+        if (offlineRecipientIds.Count == 0)
+        {
+            return;
+        }
+
+        var devices = await dbContext.PushDevices
+            .Where(x => offlineRecipientIds.Contains(x.UserId) && x.NotificationsEnabled)
+            .ToListAsync(cancellationToken);
+
+        if (devices.Count == 0)
+        {
+            return;
+        }
+
+        try
+        {
+            await pushNotificationSender.SendMessageAsync(chat, message, devices, cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            logger.LogWarning(ex, "Push dispatch failed for message {MessageId}.", message.Id);
+        }
+    }
+}

src/Massenger.Server/Infrastructure/Push/PushOptions.cs

@@ -0,0 +1,12 @@
+namespace Massenger.Server.Infrastructure.Push;
+
+public sealed class PushOptions
+{
+    public const string SectionName = "Push";
+
+    public string FirebaseProjectId { get; set; } = string.Empty;
+
+    public string ServiceAccountJsonPath { get; set; } = string.Empty;
+
+    public string ServiceAccountJson { get; set; } = string.Empty;
+}

src/Massenger.Server/Infrastructure/Storage/AttachmentStorageService.cs

@@ -0,0 +1,53 @@
+using Massenger.Server.Data.Entities;
+
+namespace Massenger.Server.Infrastructure.Storage;
+
+public sealed class AttachmentStorageService(IWebHostEnvironment environment)
+{
+    private readonly string _rootPath = Path.Combine(environment.ContentRootPath, "Data", "Attachments");
+
+    public async Task<MessageAttachment> SaveAsync(Guid messageId, IFormFile file, CancellationToken cancellationToken)
+    {
+        if (file.Length <= 0)
+        {
+            throw new InvalidOperationException("Attachment is empty.");
+        }
+
+        Directory.CreateDirectory(_rootPath);
+
+        var attachmentId = Guid.NewGuid();
+        var extension = Path.GetExtension(file.FileName);
+        var year = DateTime.UtcNow.ToString("yyyy");
+        var month = DateTime.UtcNow.ToString("MM");
+        var targetDirectory = Path.Combine(_rootPath, year, month);
+        Directory.CreateDirectory(targetDirectory);
+
+        var storedFileName = $"{attachmentId:N}{extension}";
+        var physicalPath = Path.Combine(targetDirectory, storedFileName);
+
+        await using (var source = file.OpenReadStream())
+        await using (var target = File.Create(physicalPath))
+        {
+            await source.CopyToAsync(target, cancellationToken);
+        }
+
+        return new MessageAttachment
+        {
+            Id = attachmentId,
+            MessageId = messageId,
+            OriginalFileName = string.IsNullOrWhiteSpace(file.FileName) ? "attachment" : Path.GetFileName(file.FileName),
+            ContentType = string.IsNullOrWhiteSpace(file.ContentType) ? "application/octet-stream" : file.ContentType,
+            FileSizeBytes = file.Length,
+            StoragePath = physicalPath,
+            UploadedAt = DateTimeOffset.UtcNow
+        };
+    }
+
+    public void DeleteIfExists(string? physicalPath)
+    {
+        if (!string.IsNullOrWhiteSpace(physicalPath) && File.Exists(physicalPath))
+        {
+            File.Delete(physicalPath);
+        }
+    }
+}

src/Massenger.Server/Infrastructure/Storage/DatabaseSchemaBootstrapper.cs

@@ -0,0 +1,114 @@
+using System.Data;
+using Microsoft.EntityFrameworkCore;
+using Massenger.Server.Data;
+
+namespace Massenger.Server.Infrastructure.Storage;
+
+public sealed class DatabaseSchemaBootstrapper(MassengerDbContext dbContext)
+{
+    public async Task EnsureLatestAsync(CancellationToken cancellationToken = default)
+    {
+        await EnsureMessageAttachmentsTableAsync(cancellationToken);
+        await EnsurePushDevicesTableAsync(cancellationToken);
+        await EnsureColumnAsync("Messages", "EditedAt", "TEXT NULL", cancellationToken);
+        await EnsureColumnAsync("Messages", "DeletedAt", "TEXT NULL", cancellationToken);
+    }
+
+    private async Task EnsureMessageAttachmentsTableAsync(CancellationToken cancellationToken)
+    {
+        await dbContext.Database.ExecuteSqlRawAsync(
+            """
+            CREATE TABLE IF NOT EXISTS "MessageAttachments" (
+                "Id" TEXT NOT NULL CONSTRAINT "PK_MessageAttachments" PRIMARY KEY,
+                "MessageId" TEXT NOT NULL,
+                "OriginalFileName" TEXT NOT NULL,
+                "ContentType" TEXT NOT NULL,
+                "FileSizeBytes" INTEGER NOT NULL,
+                "StoragePath" TEXT NOT NULL,
+                "UploadedAt" TEXT NOT NULL,
+                CONSTRAINT "FK_MessageAttachments_Messages_MessageId" FOREIGN KEY ("MessageId") REFERENCES "Messages" ("Id") ON DELETE CASCADE
+            );
+            """,
+            cancellationToken);
+
+        await dbContext.Database.ExecuteSqlRawAsync(
+            """
+            CREATE INDEX IF NOT EXISTS "IX_MessageAttachments_MessageId" ON "MessageAttachments" ("MessageId");
+            """,
+            cancellationToken);
+    }
+
+    private async Task EnsurePushDevicesTableAsync(CancellationToken cancellationToken)
+    {
+        await dbContext.Database.ExecuteSqlRawAsync(
+            """
+            CREATE TABLE IF NOT EXISTS "PushDevices" (
+                "Id" TEXT NOT NULL CONSTRAINT "PK_PushDevices" PRIMARY KEY,
+                "UserId" TEXT NOT NULL,
+                "Platform" INTEGER NOT NULL,
+                "InstallationId" TEXT NOT NULL,
+                "DeviceToken" TEXT NOT NULL,
+                "DeviceName" TEXT NULL,
+                "NotificationsEnabled" INTEGER NOT NULL,
+                "CreatedAt" TEXT NOT NULL,
+                "UpdatedAt" TEXT NOT NULL,
+                CONSTRAINT "FK_PushDevices_Users_UserId" FOREIGN KEY ("UserId") REFERENCES "Users" ("Id") ON DELETE CASCADE
+            );
+            """,
+            cancellationToken);
+
+        await dbContext.Database.ExecuteSqlRawAsync(
+            """
+            CREATE UNIQUE INDEX IF NOT EXISTS "IX_PushDevices_InstallationId" ON "PushDevices" ("InstallationId");
+            """,
+            cancellationToken);
+
+        await dbContext.Database.ExecuteSqlRawAsync(
+            """
+            CREATE INDEX IF NOT EXISTS "IX_PushDevices_UserId" ON "PushDevices" ("UserId");
+            """,
+            cancellationToken);
+    }
+
+    private async Task EnsureColumnAsync(
+        string tableName,
+        string columnName,
+        string definition,
+        CancellationToken cancellationToken)
+    {
+        var connection = dbContext.Database.GetDbConnection();
+        var shouldClose = connection.State != ConnectionState.Open;
+        if (shouldClose)
+        {
+            await connection.OpenAsync(cancellationToken);
+        }
+
+        try
+        {
+            await using var command = connection.CreateCommand();
+            command.CommandText = $"PRAGMA table_info(\"{tableName}\");";
+
+            await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+            while (await reader.ReadAsync(cancellationToken))
+            {
+                if (string.Equals(reader.GetString(1), columnName, StringComparison.OrdinalIgnoreCase))
+                {
+                    return;
+                }
+            }
+
+            await reader.DisposeAsync();
+
+            await using var alterCommand = connection.CreateCommand();
+            alterCommand.CommandText = $"ALTER TABLE \"{tableName}\" ADD COLUMN \"{columnName}\" {definition};";
+            await alterCommand.ExecuteNonQueryAsync(cancellationToken);
+        }
+        finally
+        {
+            if (shouldClose)
+            {
+                await connection.CloseAsync();
+            }
+        }
+    }
+}

src/Massenger.Server/Massenger.Server.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.Authentication.JwtBearer" Version="10.0.4" />
+    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.4" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="10.0.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Massenger.Shared\Massenger.Shared.csproj" />
+  </ItemGroup>
+
+</Project>

src/Massenger.Server/Massenger.Server.http

@@ -0,0 +1,6 @@
+@Massenger.Server_HostAddress = http://localhost:5289
+
+GET {{Massenger.Server_HostAddress}}/weatherforecast/
+Accept: application/json
+
+###

src/Massenger.Server/Program.cs

@@ -0,0 +1,119 @@
+using Microsoft.AspNetCore.Authentication.JwtBearer;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.IdentityModel.Tokens;
+using Massenger.Server.Data;
+using Massenger.Server.Infrastructure;
+using Massenger.Server.Infrastructure.Auth;
+using Massenger.Server.Infrastructure.Hubs;
+using Massenger.Server.Infrastructure.Push;
+using Massenger.Server.Infrastructure.Storage;
+using System.Text;
+
+var builder = WebApplication.CreateBuilder(args);
+
+builder.WebHost.UseUrls("http://0.0.0.0:5099");
+
+builder.Services.AddControllers();
+builder.Services.AddOpenApi();
+builder.Services.AddSignalR();
+builder.Services.AddEndpointsApiExplorer();
+
+builder.Services.AddDbContext<MassengerDbContext>(options =>
+    options.UseSqlite(builder.Configuration.GetConnectionString("MassengerDb") ??
+                      "Data Source=Data/massenger.db"));
+
+builder.Services.Configure<JwtOptions>(builder.Configuration.GetSection(JwtOptions.SectionName));
+builder.Services.Configure<PushOptions>(builder.Configuration.GetSection(PushOptions.SectionName));
+
+var jwtOptions = builder.Configuration
+    .GetSection(JwtOptions.SectionName)
+    .Get<JwtOptions>() ?? new JwtOptions();
+var signingKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(jwtOptions.SigningKey));
+
+builder.Services
+    .AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+    .AddJwtBearer(options =>
+    {
+        options.TokenValidationParameters = new TokenValidationParameters
+        {
+            ValidateIssuer = true,
+            ValidateAudience = true,
+            ValidateIssuerSigningKey = true,
+            ValidateLifetime = true,
+            ValidIssuer = jwtOptions.Issuer,
+            ValidAudience = jwtOptions.Audience,
+            IssuerSigningKey = signingKey,
+            ClockSkew = TimeSpan.FromSeconds(30)
+        };
+
+        options.Events = new JwtBearerEvents
+        {
+            OnMessageReceived = context =>
+            {
+                var accessToken = context.Request.Query["access_token"];
+                var path = context.HttpContext.Request.Path;
+                if (!string.IsNullOrWhiteSpace(accessToken) &&
+                    path.StartsWithSegments("/hubs/messenger"))
+                {
+                    context.Token = accessToken;
+                }
+
+                return Task.CompletedTask;
+            },
+            OnTokenValidated = async context =>
+            {
+                var principal = context.Principal;
+                if (principal is null)
+                {
+                    context.Fail("Token principal is missing.");
+                    return;
+                }
+
+                var sessionId = principal.GetRequiredSessionId();
+                var dbContext = context.HttpContext.RequestServices.GetRequiredService<MassengerDbContext>();
+                var session = await dbContext.UserSessions.SingleOrDefaultAsync(x => x.Id == sessionId, context.HttpContext.RequestAborted);
+                if (session is null)
+                {
+                    context.Fail("Session is no longer active.");
+                    return;
+                }
+
+                session.LastSeenAt = DateTimeOffset.UtcNow;
+                await dbContext.SaveChangesAsync(context.HttpContext.RequestAborted);
+            }
+        };
+    });
+
+builder.Services.AddAuthorization();
+builder.Services.AddSingleton<PresenceTracker>();
+builder.Services.AddScoped<TokenService>();
+builder.Services.AddScoped<DatabaseSeeder>();
+builder.Services.AddScoped<DatabaseSchemaBootstrapper>();
+builder.Services.AddScoped<AttachmentStorageService>();
+builder.Services.AddScoped<PushNotificationDispatcher>();
+builder.Services.AddHttpClient<IPushNotificationSender, FirebasePushNotificationSender>();
+
+var app = builder.Build();
+
+Directory.CreateDirectory(Path.Combine(app.Environment.ContentRootPath, "Data"));
+
+await using (var scope = app.Services.CreateAsyncScope())
+{
+    var db = scope.ServiceProvider.GetRequiredService<MassengerDbContext>();
+    await db.Database.EnsureCreatedAsync();
+    await scope.ServiceProvider.GetRequiredService<DatabaseSchemaBootstrapper>().EnsureLatestAsync();
+    await scope.ServiceProvider.GetRequiredService<DatabaseSeeder>().SeedAsync();
+}
+
+if (app.Environment.IsDevelopment())
+{
+    app.MapOpenApi();
+}
+
+app.UseAuthentication();
+app.UseAuthorization();
+
+app.MapControllers();
+app.MapHub<MessengerHub>("/hubs/messenger");
+
+app.Run();

src/Massenger.Server/Properties/launchSettings.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "profiles": {
+    "http": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": false,
+      "applicationUrl": "http://localhost:5099",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "Massenger.Server": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": false,
+      "applicationUrl": "http://localhost:5099",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

src/Massenger.Server/appsettings.Development.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

src/Massenger.Server/appsettings.json

@@ -0,0 +1,24 @@
+{
+  "ConnectionStrings": {
+    "MassengerDb": "Data Source=Data/massenger.db"
+  },
+  "Jwt": {
+    "Issuer": "Massenger.Server",
+    "Audience": "Massenger.Client",
+    "SigningKey": "Massenger-Replace-This-Development-Key-With-A-Long-Random-Secret-123456789",
+    "AccessTokenLifetimeMinutes": 15,
+    "RefreshTokenLifetimeDays": 30
+  },
+  "Push": {
+    "FirebaseProjectId": "",
+    "ServiceAccountJsonPath": "",
+    "ServiceAccountJson": ""
+  },
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}

src/Massenger.Shared/AttachmentKind.cs

@@ -0,0 +1,7 @@
+namespace Massenger.Shared;
+
+public enum AttachmentKind
+{
+    File = 1,
+    VoiceNote = 2
+}

src/Massenger.Shared/AuthContracts.cs

@@ -0,0 +1,13 @@
+namespace Massenger.Shared;
+
+public sealed record RegisterRequest(string Username, string DisplayName, string Password);
+
+public sealed record LoginRequest(string Username, string Password);
+
+public sealed record RefreshSessionRequest(string RefreshToken);
+
+public sealed record AuthSessionDto(
+    string AccessToken,
+    string RefreshToken,
+    DateTimeOffset AccessTokenExpiresAt,
+    UserSummaryDto User);

src/Massenger.Shared/ChatContracts.cs

@@ -0,0 +1,25 @@
+namespace Massenger.Shared;
+
+public sealed record ChatSummaryDto(
+    Guid Id,
+    string Title,
+    ChatType Type,
+    string? SecondaryText,
+    DateTimeOffset? LastActivityAt,
+    string? LastMessagePreview,
+    IReadOnlyList<UserSummaryDto> Participants,
+    bool CanSendMessages);
+
+public sealed record ChatDetailsDto(
+    Guid Id,
+    string Title,
+    ChatType Type,
+    IReadOnlyList<UserSummaryDto> Participants,
+    bool CanSendMessages,
+    IReadOnlyList<MessageDto> Messages);
+
+public sealed record CreateDirectChatRequest(Guid UserId);
+
+public sealed record CreateGroupChatRequest(string Title, IReadOnlyList<Guid> MemberIds);
+
+public sealed record CreateChannelRequest(string Title, IReadOnlyList<Guid> MemberIds);

src/Massenger.Shared/ChatType.cs

@@ -0,0 +1,8 @@
+namespace Massenger.Shared;
+
+public enum ChatType
+{
+    Direct = 1,
+    Group = 2,
+    Channel = 3
+}

src/Massenger.Shared/Massenger.Shared.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>